Use the 'pep8' in flake8.engine for testing
Use the 'pep8' in flake8.engine for testing

flake8 2.6.x uses pycodestyle, whereas prior versions used pep8.
Allow either by using the module name of `flake8.engine.pep8`
for mocking.

Also move the mocking into IntegrationTestBase.check_files.

jayvdb/flake8-putty