[Trivial] Fix testing of volume connector exception

Restore test symmetry.

Change-Id: I54a9fed73e366a30545c3cd1982588d2f544d228
(cherry picked from commit 61c5b3fd2f)

ironic/tests/unit/conductor/test_task_manager.py

@@ -279,7 +279,7 @@ class TaskManagerTestCase(db_base.DbTestCase):
         reserve_mock.assert_called_once_with(self.context, self.host,
                                              'fake-node-id')
         get_volconn_mock.assert_called_once_with(self.context, self.node.id)
-        self.assertFalse(get_voltgt_mock.called)
+        self.assertFalse(build_driver_mock.called)
         release_mock.assert_called_once_with(self.context, self.host,
                                              self.node.id)
         node_get_mock.assert_called_once_with(self.context, 'fake-node-id')