Fixes #6544 - q to receive candlepin events

This creates a queue so that katello can receive candlepin events.
It also sets config items for the queue's url and address in katello.yml so katello can
connect to the queue.
Since ```katello``` inherits from ```katello::params```, you can use ```katello::candlepin_event_queue``` even if it's not a parameter on ```katello``` but just defined in ```katello::params```. This can help you when you decide it should be a parameter.