Switch from pep8 to flake8/hacking.

Use flake8/hacking, as is standard in other OpenStack projects, but
disable new checks -- they will be enabled in later patches.

Flake8 catches many useful things
http://flake8.readthedocs.org/en/2.0/warnings.html, and hacking enforces
the OpenStack Style guidelines, including things like one import per
line and alphabetical imports in order to make merging easier.

Change-Id: Ib43f7a6790bc17c0b4efdda0a5f891b5a90303c4

tox.ini

@@ -23,13 +23,10 @@ deps=
     discover
     argparse
 
-[pep8]
-ignore = E125
-
 [testenv:pep8]
-deps = pep8
+deps = hacking>=0.5.3,<0.6
 commands =
-    pep8 --repeat --show-source --exclude=.venv,.tox,doc .
+  flake8 {posargs}
 
 [testenv:venv]
 commands = {posargs}
@@ -41,3 +38,9 @@ commands = bash -c 'if [ ! -d ./.testrepository ] ; then testr init ; fi'
 
 [tox:jenkins]
 downloadcache = ~/cache/pip
+
+[flake8]
+ignore = E125,F,H
+builtins = _
+exclude =  .venv,.git,.tox,dist,doc,*openstack/common*,*lib/python*,*egg,build
+