fixed vhost test case when the available rabbitmq cluster is in production mode (#924)

Co-authored-by: gabriel <[email protected]>

Author: knative-prow-robot

test/e2e/config/rabbitmqvhost/clustervhost.yaml

@@ -44,3 +44,4 @@ spec:
       default_permissions.configure = .*
       default_permissions.read = .*
       default_permissions.write = .*
+      loopback_users = none