Fix assert methods in unit tests

Conflicts:
  nova/tests/unit/compute/test_compute_mgr.py

  The conflict is due to not including
  I734cc01dce13f9e75a16639faf890ddb1661b7eb in stable/stein.

Change-Id: I9d77ee9007965285261362e7170114455b3bf29a
Closes-Bug: #1827984
(cherry picked from commit 3c411fe)

Author: natsumetakashi

nova/tests/unit/compute/test_compute_mgr.py

@@ -6183,7 +6183,7 @@ def test_failed_network_alloc_from_delete_raises_unexpected(self,
                         self.requested_networks, self.security_groups,
                         self.resource_provider_mapping)])
         mock_prepspawn.assert_not_called()
-        mock_failedspawn.asset_not_called()
+        mock_failedspawn.assert_not_called()
 
     @mock.patch.object(virt_driver.ComputeDriver, 'failed_spawn_cleanup')
     @mock.patch.object(virt_driver.ComputeDriver, 'prepare_for_spawn')