Turn periodic tasks off in all unit tests

We shouldn't rely on periodic tasks to randomly run in unit tests,
instead if we need them to run we should explicitly call them out.

Change-Id: I35850c47288e50d3146771dc7a9a54d62e36c3cf
Related-Bug: 1311778

nova/test.py

@@ -325,6 +325,7 @@ class TestCase(testtools.TestCase):
         CONF.set_override('fatal_exception_format_errors', True)
         CONF.set_override('enabled', True, 'osapi_v3')
         CONF.set_override('force_dhcp_release', False)
+        CONF.set_override('periodic_enable', False)
 
     def _restore_obj_registry(self):
         objects_base.NovaObject._obj_classes = self._base_test_obj_backup

nova/tests/integrated/integrated_helpers.py

@@ -69,7 +69,6 @@ class _IntegratedTestBase(test.TestCase):
         f = self._get_flags()
         self.flags(**f)
         self.flags(verbose=True)
-        self.flags(periodic_enable=False)
 
         self.useFixture(test.ReplaceModule('crypto', fake_crypto))
         nova.tests.image.fake.stub_out_image_service(self.stubs)