Fix test_list_with_limit failed

There is no action plan if creating audit was cancelled.
In this case, we just return none.

Change-Id: Ia7a93dab5978d181557d7dd7499e83655aec6f40
Closes-Bug: #1700901

watcher_tempest_plugin/tests/api/admin/base.py

@@ -232,6 +232,8 @@ class BaseInfraOptimTest(test.BaseTestCase):
         )
 
         _, action_plans = cls.client.list_action_plans(audit_uuid=audit_uuid)
+        if len(action_plans['action_plans']) == 0:
+            return
 
         return action_plans['action_plans'][0]