Add :event_catcher_openstack_service setting

Adding setting which allows switch Openstack Event provider service.

Possible values:
 * "ceilometer"
 * "panko"
 * "auto" (and any other string means auto)

config/settings.yml

@@ -1283,6 +1283,7 @@
         :poll: 10.seconds
       :event_catcher_swift:
         :poll: 10.seconds
+      :event_catcher_openstack_service: "auto"
     :queue_worker_base:
       :defaults:
         :cpu_usage_threshold: 100.percent