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
Also not sure what the policy is on specifying versions here. My understanding was that versions shouldn't normally be specified in `setup.py`. I thought the best practice was to list pinned versions in the `requirements.txt` files, so that the project can be deployed with a known working set of dependencies. And I thought  that `setup.py` normally just installs the latest versions so that we get early warning of incompatibilities with new versions of the dependency packages. @tomprince Is that right?