CORE-1544 Attempt rabbitmq start, ignore failure.

The apparent root cause behind CORE-1544 is that during the
reboot process of the controllers, ansible and os-collect-config
are racing to restart rabbitmq.  Ansible is able to correctly
restart rabbitmq, but once two of the three nodes in the cluster
are online, os-collect-config's attempt to start rabbitmq will
succeed possibly causing unexpected errors.  This change updates
the logic to ignore the failure, as well as attempts to start
rabbitmq if it is not already running.

Change-Id: Ie6aca47fbb75f2b1b8ca1fa4914b9073c0443329