Install ceilometer compute agent on nova-cpu nodes

Previously, the installation of the ceilometer compute agent was
mistakenly dropped on the floor as an unintended side effect of
the separation of rabbitmq and qpid config.

Now, this oversight is addressed, so that the compute agent is
successfully installed on nova-cpu nodes.

Change-Id: I163bafeda34fcccd749946bb109ea89cbf28393f
Closes-bug: #1318383