Checking if Loki plug-in for Docker is present and installing/updating it accordingly

[vzro]

I know this might as well be suited to becoming a module for Ansible given the length of it, however, it does work and has been rigorously tested to exhaustion and performs the aforementioned tasks, which are as follows:

1. check if loki is installed in docker

• if it is not, then install it
• if it is, then upgrade it

2. when upgrading

• first, disable the plugin
• then perform the upgrade
• finally, enable the plugin

All the commands and variables have fail-safe values and logic to make sure the tasks won't break and interrupt the execution.