Add rolling update support for nodes

[gyptazy]

General

This PR adds the basic functionality to add a rolling update support for nodes in a cluster to ProxLB.
If activated, nodes will:

• Check if update for itself is available
• Integrate the updates
• Check if a reboot is required
• Add self to ignore_nodes list
• Rebalance the cluster (move workloads away from self)
• Reboot

This also brings up the new proxlb-additions package, which adds the missing options to the Proxmox API. This packages will be required. If this option is activated but the package is missing, ProxLB will throw an error guiding you to install the required package.

Test

root@virt01:~# /bin/proxlb -d -c /etc/proxlb/proxlb.conf
<6> ProxLB: Info: [logger]: Logger verbosity got updated to: INFO.
<4> ProxLB: Warning: [api-connection]: API connection does not verify SSL certificate.
<6> ProxLB: Info: [api-connection]: API connection succeeded to host: 127.0.0.1.
<6> ProxLB: Info: [node-update-status-getter]: Get update status for node: virt01.
<6> ProxLB: Info: [node-update-status-getter]: Updates available for node: virt01.
<6> ProxLB: Info: [node-update-executor]: Execute updates on node: virt01.
<6> ProxLB: Info: [node-update-executor]: Sucessfully integrated updates to node: virt01.
<6> ProxLB: Info: [node-reboot-status-getter]: Get reboot status for node: virt01.
<6> ProxLB: Info: [node-reboot-status-getter]: No reboot required for node: virt01.
<6> ProxLB: Info: [node-statistics]: Added node virt01.
<6> ProxLB: Info: [node-statistics]: Added node virt03.
<6> ProxLB: Info: [node-statistics]: Added node virt02.
<6> ProxLB: Info: [node-statistics]: Created node statistics.
<6> ProxLB: Info: [api-get-vm-tags]: Got VM/CT tag from API.
<6> ProxLB: Info: [api-get-vm-include-exclude-tags]: Got PLB include group.
[...]

WIP

What is still missing:

• Lock that prevents other nodes to install updates in the same time
  • Avoid more load on the nodes in the cluster
  • Avoid rebooting the systems at the same time

Notes

Fixes: #39

[gyptazy]

Funny integrated in PR #48