kubernetes: fix base url for RabbitMQ management ui

kubernetes/broker-deployment.yaml

@@ -26,6 +26,8 @@ spec:
           value: "s3c0sim4!"
         - name: RABBITMQ_DEFAULT_USER
           value: villas
+        - name: RABBITMQ_SERVER_ADDITIONAL_ERL_ARGS
+          value: -rabbitmq_management path_prefix "/rabbitmq"
         ports:
         - name: web-admin
           containerPort: 15672