Turn on Flake-8 Complexity Checking

Flake8 provides the ability to measure code complexity. There are
a lot of modules in Cinder that are considered "too complex", the
worst being "cinder/tests/test_huawei_hvs.py:110:1:" with a complexity
ranking of 59.

There's some outlyers at the higher end here, but the majority of the
code checks in at under 30, so let's make that our threshold and ignore
the two offenders that are above that for now.

Granted this may or may not be valuable, but it doesn't hurt to try it
and if we all hate it or find there's no value but it makes life difficult
we can always turn it back off.

See flake8.readthedocs for more info on flake8 and McCabe complexity
checking.

Change-Id: Icc1b5f2ccf0b630c1e655f5e6abf4e25ee30afc4

cinder/tests/test_huawei_hvs.py

@@ -107,7 +107,7 @@ class FakeHVSCommon(rest_common.HVSCommon):
         # within this test.
         pass
 
-    def call(self, url=False, data=None, method=None):
+    def call(self, url=False, data=None, method=None):  # noqa
 
         url = url.replace('http://100.115.10.69:8082/deviceManager/rest', '')
         url = url.replace('/210235G7J20000000000/', '')

cinder/tests/test_netapp.py

@@ -111,7 +111,7 @@ class FakeDirectCMODEServerHandler(FakeHTTPRequestHandler):
                   '<results reason="Not supported method type"'
                   ' status="failed" errno="Not_Allowed"/></netapp>')
 
-    def do_POST(s):
+    def do_POST(s):  # noqa
         """Respond to a POST request."""
         if '/servlets/netapp.servlets.admin.XMLrequest_filer' not in s.path:
             s.send_response(404)

tox.ini

@@ -75,6 +75,7 @@ commands = {posargs}
 ignore = E251,E265,H302,H402,H405,H803,H904
 builtins = _
 exclude = .git,.venv,.tox,dist,tools,doc,common,*egg,build
+max-complexity=30
 
 [hacking]
 local-check-factory = cinder.hacking.checks.factory