Fix a test isolation error in compute.test_compute.

In the compute.test_compute tests the common notifier_api
test_notifier was being used. However, to use it correctly
requires that any existing drivers be reset, otherwise the
newly configured notifier does not take effect.

I converted the other call sites that were doing this to
also use cleanups rather than teardowns to reset it after
usage, which got rid of two boilerplate tearDown methods.

Change-Id: I6573d4652bb96dcebf38ef17d429d47d8a0e6434

nova/tests/compute/test_compute.py

@@ -103,6 +103,8 @@ class BaseTestCase(test.TestCase):
 
     def setUp(self):
         super(BaseTestCase, self).setUp()
+        notifier_api._reset_drivers()
+        self.addCleanup(notifier_api._reset_drivers)
         self.flags(compute_driver='nova.virt.fake.FakeDriver',
                    notification_driver=[test_notifier.__name__],
                    network_manager='nova.network.manager.FlatManager')
@@ -144,7 +146,6 @@ class BaseTestCase(test.TestCase):
     def tearDown(self):
         fake_image.FakeImageService_reset()
         instances = db.instance_get_all(self.context.elevated())
-        notifier_api._reset_drivers()
         for instance in instances:
             db.instance_destroy(self.context.elevated(), instance['uuid'])
         fake.restore_nodes()

nova/tests/compute/test_compute_utils.py

@@ -216,6 +216,7 @@ class UsageInfoTestCase(test.TestCase):
                        fake_get_nw_info)
 
         notifier_api._reset_drivers()
+        self.addCleanup(notifier_api._reset_drivers)
         self.flags(use_local=True, group='conductor')
         self.flags(compute_driver='nova.virt.fake.FakeDriver',
                    notification_driver=[test_notifier.__name__],
@@ -233,10 +234,6 @@ class UsageInfoTestCase(test.TestCase):
                        'show', fake_show)
         fake_network.set_stub_network_methods(self.stubs)
 
-    def tearDown(self):
-        notifier_api._reset_drivers()
-        super(UsageInfoTestCase, self).tearDown()
-
     def _create_instance(self, params={}):
         """Create a test instance"""
         inst = {}

nova/tests/test_notifications.py

@@ -55,6 +55,7 @@ class NotificationsTestCase(test.TestCase):
         fake_network.set_stub_network_methods(self.stubs)
 
         notifier_api._reset_drivers()
+        self.addCleanup(notifier_api._reset_drivers)
         self.flags(compute_driver='nova.virt.fake.FakeDriver',
                    notification_driver=[test_notifier.__name__],
                    network_manager='nova.network.manager.FlatManager',
@@ -68,10 +69,6 @@ class NotificationsTestCase(test.TestCase):
 
         self.instance = self._wrapped_create()
 
-    def tearDown(self):
-        notifier_api._reset_drivers()
-        super(NotificationsTestCase, self).tearDown()
-
     def _wrapped_create(self, params=None):
         inst = {}
         inst['image_ref'] = 1