Add integration tests for plugin system

[Hornwitser]

There are no tests currently covering if plugins are loaded, this task consists of the following items:

• Create a test plugin in test/files
• Add it to be loaded in test/integration/index.js
• Add a clusterctl command to it and test that it's present in test/integration/clusterio.js
• Add a control-controller request and test that it works.
• Add a controller-host event and test that BaseControlPlugin.broadcastEventToHosts work.
• Add a control-host request and test that it works.
• Add a control-instance request and test that it works on a running instance.
• Add a Lua module to the plugin and use a request like the previous entry to test that it is present with an rcon command.
• Add a request producing log statements in the plugin at the controller, host and instances level and verify log messages are correctly tagged with the plugin and host/instance id for the host/instance plugin code.