wrap lint/tests in tox environments

* got rid of .pep8, the configuration is now done in a [pep8] section of
  tox.ini which recent version of pep8 uses
* add support for flake8, a wrapper around pep8 and pyflakes which also
  introduces its own tests
* envs for py26 and py27 testing

The user configuration file is not generated yet :/

Change-Id: Ic8dfb837d21879f0d2aa70c6647a5a941a7bf2d7
Merge "wrap lint/tests in tox environments"