out of order execution of bash script in build_debian.sh

[lguohan]

Description
It looks like there are out of execution in build_debian.sh

This issue is suspected to be related to this commit id. a799669

Failed cases:
https://sonic-jenkins.westus2.cloudapp.azure.com/job/mellanox/job/buildimage-mlnx-all-pr/3099/console

In this case, the user add is executed before installing docker-engine

Processing triggers for libc-bin (2.24-11+deb9u3) ...
Processing triggers for systemd (232-25+deb9u4) ...
+ docker_deb_url=https://apt.dockerproject.org/repo/pool/main/d/docker-engine/docker-engine_1.11.1-0~stretch_amd64.deb
++ mktemp
+ docker_deb_temp=/tmp/tmp.hKEP30LM1Z
+ trap_push 'rm -f /tmp/tmp.hKEP30LM1Z'
+ local 'oldcmd=sudo umount $FILESYSTEM_ROOT/proc || true; true'
+ local 'newcmd=rm -f /tmp/tmp.hKEP30LM1Z; sudo umount $FILESYSTEM_ROOT/proc || true; true'
+ trap -- 'rm -f /tmp/tmp.hKEP30LM1Z; sudo umount $FILESYSTEM_ROOT/proc || true; true' EXIT INT TERM HUP
+ _trap_push 'rm -f /tmp/tmp.hKEP30LM1Z; sudo umount $FILESYSTEM_ROOT/proc || true; true'
+ local 'next=rm -f /tmp/tmp.hKEP30LM1Z; sudo umount $FILESYSTEM_ROOT/proc || true; true'
++ echo 'rm -f /tmp/tmp.hKEP30LM1Z; sudo umount $FILESYSTEM_ROOT/proc || true; true'
++ sed -e 's/'\''/'\''\\'\'''\''/g'
+ eval 'trap_push() {
        local oldcmd='\''rm -f /tmp/tmp.hKEP30LM1Z; sudo umount $FILESYSTEM_ROOT/proc || true; true'\''
        local newcmd="$1; $oldcmd"
        trap -- "$newcmd" EXIT INT TERM HUP
        _trap_push "$newcmd"
    }'
+ wget https://apt.dockerproject.org/repo/pool/main/d/docker-engine/docker-engine_1.11.1-0~stretch_amd64.deb -qO /tmp/tmp.hKEP30LM1Z
+ sudo mkdir -p ./fsroot/etc/systemd/system/docker.service.d/
+ sudo cp files/docker/docker.service.conf ./fsroot/etc/systemd/system/docker.service.d/
+ sudo LANG=C chroot ./fsroot useradd -G sudo,docker admin -c 'Default admin user,,,' -m -s /bin/bash
useradd: group 'docker' does not exist

Here is the correct case. the useradd is after the docker-engine installation.
https://sonic-jenkins.westus2.cloudapp.azure.com/job/mellanox/job/buildimage-mlnx-all/701/artifact/target/sonic-mellanox.bin.log

+ docker_deb_url=https://apt.dockerproject.org/repo/pool/main/d/docker-engine/docker-engine_1.11.1-0~stretch_amd64.deb
++ mktemp
+ docker_deb_temp=/tmp/tmp.BVnnqiOOzm
+ trap_push 'rm -f /tmp/tmp.BVnnqiOOzm'
+ local 'oldcmd=sudo umount $FILESYSTEM_ROOT/proc || true; true'
+ local 'newcmd=rm -f /tmp/tmp.BVnnqiOOzm; sudo umount $FILESYSTEM_ROOT/proc || true; true'
+ trap -- 'rm -f /tmp/tmp.BVnnqiOOzm; sudo umount $FILESYSTEM_ROOT/proc || true; true' EXIT INT TERM HUP
+ _trap_push 'rm -f /tmp/tmp.BVnnqiOOzm; sudo umount $FILESYSTEM_ROOT/proc || true; true'
+ local 'next=rm -f /tmp/tmp.BVnnqiOOzm; sudo umount $FILESYSTEM_ROOT/proc || true; true'
++ echo 'rm -f /tmp/tmp.BVnnqiOOzm; sudo umount $FILESYSTEM_ROOT/proc || true; true'
++ sed -e 's/'\''/'\''\\'\'''\''/g'
+ eval 'trap_push() {
        local oldcmd='\''rm -f /tmp/tmp.BVnnqiOOzm; sudo umount $FILESYSTEM_ROOT/proc || true; true'\''
        local newcmd="$1; $oldcmd"
        trap -- "$newcmd" EXIT INT TERM HUP
        _trap_push "$newcmd"
    }'
+ wget https://apt.dockerproject.org/repo/pool/main/d/docker-engine/docker-engine_1.11.1-0~stretch_amd64.deb -qO /tmp/tmp.BVnnqiOOzm
+ sudo dpkg --root=./fsroot -i /tmp/tmp.BVnnqiOOzm
Selecting previously unselected package docker-engine.
(Reading database ... 12981 files and directories currently installed.)
Preparing to unpack /tmp/tmp.BVnnqiOOzm ...
Unpacking docker-engine (1.11.1-0~stretch) ...
dpkg: dependency problems prevent configuration of docker-engine:
 docker-engine depends on iptables; however:
  Package iptables is not installed.
 docker-engine depends on libltdl7 (>= 2.4.6); however:
  Package libltdl7 is not installed.

dpkg: error processing package docker-engine (--install):
 dependency problems - leaving unconfigured
Processing triggers for systemd (232-25+deb9u4) ...
Errors were encountered while processing:
 docker-engine
+ sudo LANG=C DEBIAN_FRONTEND=noninteractive chroot ./fsroot apt-get -y install -f
Reading package lists...
Building dependency tree...
Reading state information...
Correcting dependencies... Done
The following additional packages will be installed:
  iptables libip6tc0 libiptc0 libltdl7 libmnl0 libnetfilter-conntrack3
  libnfnetlink0 libxtables12
The following NEW packages will be installed:
  iptables libip6tc0 libiptc0 libltdl7 libmnl0 libnetfilter-conntrack3
  libnfnetlink0 libxtables12
0 upgraded, 8 newly installed, 0 to remove and 2 not upgraded.
1 not fully installed or removed.
Need to get 943 kB of archives.
After this operation, 2584 kB of additional disk space will be used.
Get:1 http://debian-archive.trafficmanager.net/debian stretch/main amd64 libip6tc0 amd64 1.6.0+snapshot20161117-6 [68.1 kB]
Get:2 http://debian-archive.trafficmanager.net/debian stretch/main amd64 libiptc0 amd64 1.6.0+snapshot20161117-6 [57.5 kB]
Get:3 http://debian-archive.trafficmanager.net/debian stretch/main amd64 libxtables12 amd64 1.6.0+snapshot20161117-6 [75.9 kB]
Get:4 http://debian-archive.trafficmanager.net/debian stretch/main amd64 libmnl0 amd64 1.0.4-2 [12.2 kB]
Get:5 http://debian-archive.trafficmanager.net/debian stretch/main amd64 libnfnetlink0 amd64 1.0.1-3 [13.5 kB]
Get:6 http://debian-archive.trafficmanager.net/debian stretch/main amd64 libnetfilter-conntrack3 amd64 1.0.6-2 [38.7 kB]
Get:7 http://debian-archive.trafficmanager.net/debian stretch/main amd64 iptables amd64 1.6.0+snapshot20161117-6 [288 kB]
Get:8 http://debian-archive.trafficmanager.net/debian stretch/main amd64 libltdl7 amd64 2.4.6-2 [389 kB]
debconf: delaying package configuration, since apt-utils is not installed
Fetched 943 kB in 0s (5956 kB/s)
E: Can not write log (Is /dev/pts mounted?) - posix_openpt (19: No such device)
Selecting previously unselected package libip6tc0:amd64.
(Reading database ... 13085 files and directories currently installed.)
Preparing to unpack .../0-libip6tc0_1.6.0+snapshot20161117-6_amd64.deb ...
Unpacking libip6tc0:amd64 (1.6.0+snapshot20161117-6) ...
Selecting previously unselected package libiptc0:amd64.
Preparing to unpack .../1-libiptc0_1.6.0+snapshot20161117-6_amd64.deb ...
Unpacking libiptc0:amd64 (1.6.0+snapshot20161117-6) ...
Selecting previously unselected package libxtables12:amd64.
Preparing to unpack .../2-libxtables12_1.6.0+snapshot20161117-6_amd64.deb ...
Unpacking libxtables12:amd64 (1.6.0+snapshot20161117-6) ...
Selecting previously unselected package libmnl0:amd64.
Preparing to unpack .../3-libmnl0_1.0.4-2_amd64.deb ...
Unpacking libmnl0:amd64 (1.0.4-2) ...
Selecting previously unselected package libnfnetlink0:amd64.
Preparing to unpack .../4-libnfnetlink0_1.0.1-3_amd64.deb ...
Unpacking libnfnetlink0:amd64 (1.0.1-3) ...
Selecting previously unselected package libnetfilter-conntrack3:amd64.
Preparing to unpack .../5-libnetfilter-conntrack3_1.0.6-2_amd64.deb ...
Unpacking libnetfilter-conntrack3:amd64 (1.0.6-2) ...
Selecting previously unselected package iptables.
Preparing to unpack .../6-iptables_1.6.0+snapshot20161117-6_amd64.deb ...
Unpacking iptables (1.6.0+snapshot20161117-6) ...
Selecting previously unselected package libltdl7:amd64.
Preparing to unpack .../7-libltdl7_2.4.6-2_amd64.deb ...
Unpacking libltdl7:amd64 (2.4.6-2) ...
Processing triggers for libc-bin (2.24-11+deb9u3) ...
Setting up libxtables12:amd64 (1.6.0+snapshot20161117-6) ...
Setting up libltdl7:amd64 (2.4.6-2) ...
Setting up libnfnetlink0:amd64 (1.0.1-3) ...
Setting up libmnl0:amd64 (1.0.4-2) ...
Setting up libip6tc0:amd64 (1.6.0+snapshot20161117-6) ...
Setting up libnetfilter-conntrack3:amd64 (1.0.6-2) ...
Setting up libiptc0:amd64 (1.6.0+snapshot20161117-6) ...
Setting up iptables (1.6.0+snapshot20161117-6) ...
Setting up docker-engine (1.11.1-0~stretch) ...
Created symlink /etc/systemd/system/multi-user.target.wants/docker.service -> /lib/systemd/system/docker.service.
Created symlink /etc/systemd/system/sockets.target.wants/docker.socket -> /lib/systemd/system/docker.socket.
Running in chroot, ignoring request.
Processing triggers for libc-bin (2.24-11+deb9u3) ...
Processing triggers for systemd (232-25+deb9u4) ...
+ sudo mkdir -p ./fsroot/etc/systemd/system/docker.service.d/
+ sudo cp files/docker/docker.service.conf ./fsroot/etc/systemd/system/docker.service.d/
+ sudo LANG=C chroot ./fsroot useradd -G sudo,docker admin -c 'Default admin user,,,' -m -s /bin/bash

Steps to reproduce the issue:
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Describe the results you received:

Describe the results you expected:

Additional information you deem important (e.g. issue happens only occasionally):

**Output of `show version`:**

```
(paste your output here)
```

**Attach debug file `sudo generate_dump`:**

```
(paste your output here)
```