Fix the tempest that checks executing Mistral twice

Change-Id: Ia7c12168c10c84e1bfc38fd1b70b8b987f6ed8af

vitrage_tempest_plugin/tests/notifiers/test_mistral_notifier.py

@@ -13,6 +13,8 @@
 # under the License.
 
 import json
+import time
+
 from oslo_log import log as logging
 from testtools.matchers import HasLength
 
@@ -119,6 +121,8 @@ class TestMistralNotifier(BaseTestEvents):
             if template:
                 v_utils.delete_template(template['uuid'])   # no longer needed
 
+        time.sleep(2)   # wait for the evaluator to process the new template
+
         # Verify that there is an execution for every instance
         executions = self.mistral_client.executions.list()
         self.assertIsNotNone(executions,