Fix mock.patch usage in unit tests

There are various places where a patcher was started but never stopped
or the test stopped the wrong thing. This causes that the mocking is not
removed at the end of the test case execution. So the subsequnet test
cases executed by the same executor will see the same mocked function.
Depending on the test case exection order it can lead to intermittent
test failures.

Change-Id: I8e66154c19c125f3093c8a1990b0c79332996560

nova/tests/unit/compute/test_compute.py

@@ -8373,9 +8373,11 @@ class ComputeAPITestCase(BaseTestCase):
                                    'schedule_and_build_instances',
                                    autospec=True)
         self.schedule_and_build_instances_mock = _patch.start()
+        self.addCleanup(_patch.stop)
         _patch = mock.patch.object(self.compute_api.compute_task_api,
                                    'rebuild_instance', autospec=True)
         self.rebuild_instance_mock = _patch.start()
+        self.addCleanup(_patch.stop)
 
         # Assume that we're always OK for network quota.
         def fake_validate_networks(context, requested_networks, num_instances):

nova/tests/unit/pci/fakes.py

@@ -33,6 +33,8 @@ def patch_pci_whitelist(f):
     @functools.wraps(f)
     def wrapper(self, *args, **kwargs):
         patcher = fake_pci_whitelist()
-        f(self, *args, **kwargs)
-        patcher.stop()
+        try:
+            f(self, *args, **kwargs)
+        finally:
+            patcher.stop()
     return wrapper

nova/tests/unit/scheduler/client/test_report.py

@@ -1058,9 +1058,10 @@ class TestSetAndClearAllocations(SchedulerReportClientTestCase):
         super(TestSetAndClearAllocations, self).setUp()
         # We want to reuse the mock throughout the class, but with
         # different return values.
-        self.mock_post = mock.patch(
-            'nova.scheduler.client.report.SchedulerReportClient.post').start()
-        self.addCleanup(self.mock_post.stop)
+        patcher = mock.patch(
+            'nova.scheduler.client.report.SchedulerReportClient.post')
+        self.mock_post = patcher.start()
+        self.addCleanup(patcher.stop)
         self.mock_post.return_value.status_code = 204
         self.rp_uuid = mock.sentinel.rp
         self.consumer_uuid = mock.sentinel.consumer

nova/tests/unit/volume/test_cinder.py

@@ -989,10 +989,11 @@ class CinderClientTestCase(test.NoDBTestCase):
         self.ctxt = context.RequestContext('fake-user', 'fake-project')
         # Mock out the keystoneauth stuff.
         self.mock_session = mock.Mock(autospec=session.Session)
-        load_session = mock.patch('keystoneauth1.loading.'
+        patcher = mock.patch('keystoneauth1.loading.'
                                   'load_session_from_conf_options',
-                                  return_value=self.mock_session).start()
-        self.addCleanup(load_session.stop)
+                                  return_value=self.mock_session)
+        patcher.start()
+        self.addCleanup(patcher.stop)
 
     @mock.patch('cinderclient.client.get_volume_api_from_url',
                 return_value='3')