Add RabbitMQ system level upgrade metadata

Change-Id: I792c942ad424b3a8c3930062b8cada8f9edd8f0f
Related-Prod: PROD-29461
(cherry picked from commit 757f653dfee6166a39eb0bcf4226472495070aee)
diff --git a/rabbitmq/server/single.yml b/rabbitmq/server/single.yml
index 6183f81..9982957 100644
--- a/rabbitmq/server/single.yml
+++ b/rabbitmq/server/single.yml
@@ -1,2 +1,3 @@
 classes:
 - service.rabbitmq.server.single
+- system.rabbitmq.upgrade