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.
@ehelms created  qpid_url in katello::params and moved both candlepin_event_queue into katello::params.
@ekohl not sure why but when I use katello::candlepin_event_queue it says that 
'Could not look up qualified variable 'katello::candlepin_event_queue'; class katello has not been evaluated'