allow overriding functional arguments with posargs

It is useful to run a single test from the command line with, for instance:

  tox -e ansibledevel-functional -- -k 'test_command_init_role[docker]' test/functional/test_command.py

The test/functional/ pytest argument is made a default used when there
are no posargs instead of being hardcoded and always used. If all
pytest invocations include test/functional/ there is no way for the
user to restrict the tests being run to a single file.

Signed-off-by: singuliere <[email protected]>

tox.ini

@@ -30,7 +30,7 @@ extras =
     vagrant
 commands =
     unit: pytest test/unit/ --cov={toxinidir}/molecule/ --no-cov-on-fail {posargs}
-    functional: pytest test/functional/ {posargs}
+    functional: pytest {posargs:test/functional/}
     lint: flake8
     lint: yamllint -s test/ molecule/