A few cleanups

* Removed a comment about rabbit being installed for use by sensu.
  That is currently only true in the test environment, and I would
  like to change that.
* Removed pacemaker/corosync from site.yml.
* Removed pacemaker/corosync openstack-ha playbook.  We are not using
  this, if we want to use it, we can always pull it back in.