API Tests: Ensure updated_time changes in stack patch update

Check that the patch update has actually run and that we're not simply
looking at the UPDATE_COMPLETE status from the previous test, otherwise
the outputs may not have been updated before we run the next test.

Change-Id: Ia45a303e74e19e7d1887c4e242a8ee5655208e59
Closes-Bug: #1721692
diff --git a/api/gabbits/stacks.yaml b/api/gabbits/stacks.yaml
index b37eabd..f37f7a1 100644
--- a/api/gabbits/stacks.yaml
+++ b/api/gabbits/stacks.yaml
@@ -138,6 +138,7 @@
     delay: 1.0
   response_json_paths:
     $.stack.stack_status: UPDATE_COMPLETE
+    $.stack.updated_time: /(?!$HISTORY['poll for stack UPDATE_COMPLETE'].$RESPONSE['$.stack.updated_time'])/
 
 - name: list stack outputs
   GET: $LAST_URL/outputs