Remove glance_notifications from notification_topic

The default notification_topic in Glance has been changed from
'glance_notifications' to 'notifications' in grizzly-2.

Ceilometer was configured to also listen on the
'glance_notifications' notification_topic in addition to
'notifications' to patch this bug. It shouldn't anymore.

Change-Id: I3d797c7e849319a1e20ef3ecbf158e8b8579d450
Closes-bug: #1273876
(cherry picked from commit 924f18ffae174847d4c3d5ec5d5ae4241c9dd897)
Merge "Remove glance_notifications from notification_topic" into stable/havana