Set glance control_exchange to 'glance'

Glance control_exchange in glance-api.conf wasn't set
and glance used default value for this - 'openstack'.
So, exchange 'glance' and queue 'glance' didn't exist in rabbit.
But ceilometer as default glance control exchange uses 'glance'.
This patch fixes this problem.

Change-Id: Iac363ba3f95a300c416dbfd94e37d21f5f9cef40
Closes-bug: #1335891
Merge "Set glance control_exchange to 'glance'"