Allow fast finish up travis builds

As soon as one part of the build has failed,
the job will be marked as a failure and appear
red in github.

See: http://about.travis-ci.org/blog/2013-11-27-fast-finishing-builds
Move flake8 checks to before_install
Running Python first for flake8
Merge pull request #1847 from joshmoore/travis-fast-finish

Allow fast finish up travis builds