`patch_cover` checks to make sure your patch has
adequate test coverage.
How it works is it stashes your changes, runs `tox -e cover`,
saves the results then stash pops your change and runs cover
again. It then reports to show if your code in your patch
has 100% test coverage or not.
The intent of this job is to be a non-voting / warning like
job that can inform reviewers if the review clearly needs
more testing.
Since cover.sh is copied from [0] the copyright should
reflect the owners of the code.
[0]: https://github.com/openstack/rally/blob/master/tests/ci/cover.sh
Change-Id: I66572072aa4d9563b6e1f73a8f8b3437116ef3c4