Enable some off-by-default checks

Some of the available checks are disabled by default, like:
[H203] Use assertIs(Not)None to check for None

Change-Id: I59dafb62cedc5217b6e5eb6efb997a9ee3c29bbb

openstackclient/tests/functional/volume/v1/test_service.py

@@ -64,10 +64,7 @@ class VolumeServiceTests(common.BaseVolumeTests):
             'enabled',
             cmd_output[0]['Status']
         )
-        self.assertEqual(
-            None,
-            cmd_output[0]['Disabled Reason']
-        )
+        self.assertIsNone(cmd_output[0]['Disabled Reason'])
 
         # Test volume service set --disable and --disable-reason
         disable_reason = 'disable_reason'

openstackclient/tests/functional/volume/v2/test_service.py

@@ -64,8 +64,7 @@ class VolumeServiceTests(common.BaseVolumeTests):
             'enabled',
             cmd_output[0]['Status']
         )
-        self.assertEqual(
-            None,
+        self.assertIsNone(
             cmd_output[0]['Disabled Reason']
         )
 

tox.ini

@@ -85,6 +85,8 @@ commands = sphinx-build -a -E -W -d releasenotes/build/doctrees -b html releasen
 
 [flake8]
 show-source = True
+# H203: Use assertIs(Not)None to check for None
+enable-extensions = H203
 exclude = .git,.tox,dist,doc,*lib/python*,*egg,build,tools
 # If 'ignore' is not set there are default errors and warnings that are set
 # Doc: http://flake8.readthedocs.org/en/latest/config.html#default