Enable some serivce when on boot

Solve the devstack ./rejoin-stack.sh when is reboot-safe in RHEL 7.
Enable mysql, postgresql, rabbitmq-server, openvswitch service when on boot.

Change-Id: I3ce9fc58ccc76092ad08314de1c3c9339ebfb3b5
Related-Bug: #1486833
diff --git a/lib/rpc_backend b/lib/rpc_backend
index 03eacd8..2e1c897 100644
--- a/lib/rpc_backend
+++ b/lib/rpc_backend
@@ -48,6 +48,9 @@
         # Install rabbitmq-server
         install_package rabbitmq-server
     fi
+    if is_fedora; then
+        sudo systemctl enable rabbitmq-server
+    fi
 }
 
 # restart the rpc backend