With HA, really wait for rabbitmq to be started

Until now, we were just checking that pacemaker has marked the resource
has started. But what we really want is to start making use of rabbitmq,
and it sometimes happen that rabbitmq is still starting while we try to
add the vhost and so on.

So on top of waiting for pacemaker to mark the resource as started, also
wait for "rabbitmqctl list_vhosts" to tell us that it is really started.
This makes the wait more synchronous, like the init script.

Note that we do not use "rabbitmqctl status" as this command seems to
tell us rabbitmq is ready slightly before it's fully ready, causing a
race.

This is also similar to what we do with postgresql, where we try to
connect to it when checking it's running.