Don't run requirements pep8/py27 on Folsom/Grizzly

The tox.ini and test files were not backported to the
openstack/requirements stable branches (Folsom and Grizzly). Disable the
two tests that depend on those files so that changes can be merged to
the stable branches.

Change-Id: I92be6f28687385ad12e49fa3f666b049742dc354