replaces pyflakes with flake8 in tox, modifies various flocker/ source

replaces pyflakes with flake8 in tox, modifies various flocker/ source files for PEP8 compatibility

https://github.com/hybridlogic/flocker/issues/35

http://build.flocker.hybridcluster.net/boxes-flocker?branch=pyflakes-flake8-35
So now you've found a way to ignore this file, we should revert all these changes. Just replace with the _version.py from master.