Start using Pyflakes and Hacking

Instead of globally ignoring pyflakes and
hacking warnings, only blacklist those that trigger
very frequently so far, in order to clean them
up in followup commits. Fix and start gating
on the rest already.

Change-Id: Ied7c7250061e3bf379e8286e8ce3b9e4af817faf

tests/test_shell.py

@@ -16,9 +16,7 @@
 # vim: tabstop=4 shiftwidth=4 softtabstop=4
 
 import argparse
-import cStringIO
 import os
-import sys
 
 from glanceclient import exc
 from glanceclient import shell as openstack_shell