Remove optional notifier keys from glance

In the glance chapter of the installation guide, we configure
the notifier to use messaging. Glance notifications only appear
useful to environments using the glance ceilometer agent. Not
all environments use ceilometer and the associated queue could
become large without a consumer. We can remove the notifier keys
from the glance chapter since the glance ceilometer agent section
includes them.

Change-Id: I186cf4e54fa5e6c1389be2b5ea33d124abb483ff
Closes-Bug: #1360552
Merge "Remove optional notifier keys from glance"