FC-38 System events and handlers for blue-green deployment

Handlers for new system events have been added, but they do not have any action yet.
Also corrected an issue where rate limiter was applied for ignored messages.

Signed-off-by: Steffan Westcott <steffan.westcott@clicktravel.com>
I am about to refactor message handling, the class MessageHandlingWorker may in fact disappear. It was not worthwhile refactoring this test in the meantime.