Fix mock aws teardown in awskinesis tests

We need to stop AWS after the rest of the test shutdown procedure,
otherwise we will attempt to make unauthenticated calls to AWS.
This change adjusts the shutdown order in the aws kinesis tests
to run the mock aws shutdown last.

Change-Id: Ie50db58f7271a85da1e47fc4faeb0133013d1296

tests/unit/test_gerrit_awskinesis.py

@@ -50,12 +50,9 @@ class TestGerritEventSourceAWSKinesis(ZuulTestCase):
                 'StreamMode': 'ON_DEMAND'
             }
         )
+        self.addCleanup(self.mock_aws.stop)
         super().setUp()
 
-    def tearDown(self):
-        self.mock_aws.stop()
-        super().tearDown()
-
     @simple_layout('layouts/simple.yaml')
     def test_kinesis(self):
         listener = self.fake_gerrit.event_thread