Make pep8 *the* linting interface
Make pep8 *the* linting interface

According to the PTI (=Python Test Interface,
http://governance.openstack.org/reference/cti/python_cti.html), pep8
is the interface for codestyle checks. Move all tests from linters to
pep8.

This change will be followed by a change to project-config to use pep8
for testing in the gate.

Needed-By: I87b7015338bbd9fc0bebdf45af3c974ff2d03945
Change-Id: Ic5f26e2e0d92dfa4ee0e0962f4d27cdd5961415f

openstack/steth,openstack/steth