Fix iNotifyWatch timeout

[pdhamdhere]

Install Watch before we issue attach so that we don't miss it.

Testing (manual):
Without this change, docker volume create -d vsphere vol1 would consistently timeout with following logs;

2017-03-21 02:49:40.042231308 +0000 UTC [INFO] Attaching volume and creating filesystem name=tv6 fstype=ext4 
2017-03-21 02:49:40.042930043 +0000 UTC [DEBUG] vmdkOps.Attach name=tv6
2017-03-21 02:49:50.463992516 +0000 UTC [WARNING] Exceeded timeout while waiting for device attach to completetimeout=10s device="/dev/disk/by-path/pci-0000:0b:00.0-scsi-0:0:2:0" 

With this change, it succeeds;

2017-03-21 03:04:38.576935001 +0000 UTC [INFO] Attaching volume and creating filesystem fstype=ext4 name=tv1 
2017-03-21 03:04:38.578020905 +0000 UTC [DEBUG] vmdkOps.Attach name=tv1
2017-03-21 03:04:38.940107037 +0000 UTC [DEBUG] event: "/dev/disk/by-path/pci-0000:0b:00.0-scsi-0:0:1:0": 0x100 == IN_CREATE
2017-03-21 03:04:38.940679315 +0000 UTC [INFO] Scan complete device="/dev/disk/by-path/pci-0000:0b:00.0-scsi-0:0:1:0" event="/dev/disk/by-path/pci-0000:0b:00.0-scsi-0:0:1:0": 0x100 == IN_CREATE 

[lipingxue]

@pdhamdhere Do you have an issue for this PR? What is the problem the PR tries to fix?

[pdhamdhere]

Fixes #962

[msterin]

Aha ! Another race defeated :-)

Thanks for closing up on this one !