Configure travis to use flake8 instead of pep8 and pyflakes

* Remove unused import

Change-Id: Id1844c48abe013520238fb463b91ce8bdd70ad7c
Signed-off-by: Rosario Di Somma <rosario.disomma@dreamhost.com>
Merge pull request #15 from rodis/feature/move-travis-to-flake8

Configure travis to use flake8 instead of pep8 and pyflakes