The 'tox -epep8' command takes a long time as it checks
every single file in the Nova git repository (~1,400 at
time of writing).
This makes tox use a simple wrapper around flake8 which
can be told to restrict the check to only files changed
in the current command. This can be invoked in a simple
manner with 'tox -epep8 -- -HEAD'. Since most commits
only touch a handful of files, this will usually be
far faster than checking all 1,400 source files.
To check an entire branch for bisectability it can be
automated via
git rebase -i master -x 'tox -epep8 -- -HEAD'
Change-Id: I157d1ccb883ca02402eee51fd7d6a50f86079389
a7471dd773