tox: Optionally specify a file with the pep8 and lint environments

So developers can do things like:

  $ tox -e pep8 patchwork/tests/test_rest.py

or:

  $ tox -e lint patchwork/tests/test_rest.py

Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>

tox.ini

@@ -23,7 +23,7 @@ passenv =
 [testenv:pep8]
 basepython = python2.7
 deps = flake
-commands = flake8 {posargs} patchwork
+commands = flake8 {posargs:patchwork}
 
 [flake8]
 ignore = E121,E122,E123,E124,E125,E126,E127,E128,E129,E131,E251,H405
@@ -34,7 +34,7 @@ basepython = python2.7
 deps =
     pylint
     -r{toxinidir}/docs/requirements-prod.txt
-commands = pylint patchwork --rcfile=pylint.rc
+commands = pylint {posargs:patchwork} --rcfile=pylint.rc
 
 [testenv:coverage]
 basepython = python2.7