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

tox.ini

@@ -1,5 +1,5 @@
 [tox]
-envlist = py26,py27,linters
+envlist = py26,py27,pep8
 
 [testenv]
 setenv = VIRTUAL_ENV={envdir}
@@ -19,10 +19,16 @@ whitelist_externals = *
 [testenv:venv]
 commands = {posargs}
 
+# Temporary environment until infra jobs are changed.
+# TODO(jaegerandi): remove this
 [testenv:linters]
 commands = flake8
 distribute = false
 
+[testenv:pep8]
+commands = flake8
+distribute = false
+
 [flake8]
 ignore = H703,H102,E265,E262,H233
 show-source = true