Enable some off-by-default checks

Some of the available checks are disabled by default, like:
[H106] Don’t put vim configuration in source files
[H203] Use assertIs(Not)None to check for None

Change-Id: I815f189258356cb911d1e232b6f53c864e53c602

heatclient/tests/unit/test_utils.py

@@ -415,8 +415,7 @@ class TestURLFunctions(testtools.TestCase):
                          tmpl_url)
         self.assertEqual(utils.get_template_url(None, tmpl_url),
                          tmpl_url)
-        self.assertEqual(utils.get_template_url(None, None),
-                         None)
+        self.assertIsNone(utils.get_template_url(None, None))
 
     def test_base_url_for_url(self):
         self.assertEqual(

tox.ini

@@ -49,6 +49,7 @@ commands=
 
 [flake8]
 show-source = True
+enable-extensions = H203,H106
 exclude=.venv,.git,.tox,dist,*lib/python*,*egg,build
 max-complexity=20