rabbitmq: Allow automatic cluster recovery before forcing it

When joining a node into an existing cluster, check to see if it is
already clustered before force removing it from the cluster and
re-adding.  If the clustering is already functional there's no need to
force it again.

heartbeat/rabbitmq-cluster

@@ -238,6 +238,11 @@ rmq_start_first()
 	return $rc
 }
 
+rmq_is_clustered()
+{
+    $RMQ_CTL eval 'rabbit_mnesia:is_clustered().' | grep -q true
+}
+
 rmq_join_existing()
 {
 	local join_list="$1"
@@ -249,6 +254,11 @@ rmq_join_existing()
 		return $OCF_ERR_GENERIC
 	fi
 
+        if rmq_is_clustered; then
+            ocf_log info "Successfully re-joined existing rabbitmq cluster automatically"
+            return $OCF_SUCCESS
+        fi
+
 	# unconditionally join the cluster
 	$RMQ_CTL stop_app > /dev/null 2>&1
 	for node in $(echo "$join_list"); do