'tox -e py27' failed

cfg.CONF.debug should be set False as default,
If it's True, some unittests can't pass.

Change-Id: Ib098250af3aec48aa9d9152e20c80460f3bd641e
Closes-Bug: #1625560

watcher/tests/api/test_hooks.py

@@ -120,6 +120,7 @@ class TestNoExceptionTracebackHook(base.FunctionalTest):
         p = mock.patch.object(root.Root, 'convert')
         self.root_convert_mock = p.start()
         self.addCleanup(p.stop)
+        cfg.CONF.set_override('debug', False, enforce_type=True)
 
     def test_hook_exception_success(self):
         self.root_convert_mock.side_effect = Exception(self.MSG_WITH_TRACE)