Allow event_pipeline.yaml to have publishers specified. This is
required to support aodh event alarms by pushing notifications
to an alarm queue as described here:
http://docs.openstack.org/developer/aodh/event-alarm.html
Change-Id: If367192f9c0214b3b4462788024dd9222dff558e
Signed-off-by: Michael Chapman <woppin@gmail.com>