remove python setup.py test

Removed the "python setup.py test" feature in favor of a straight run of
"tox".   Per Pypa / pytest developers, "setup.py" commands are in general
headed towards deprecation in favor of tox.  The tox.ini script has been
updated such that running "tox" with no arguments will perform a single run
of the test suite against the default installed Python interpreter.

.. seealso::

https://github.com/pypa/setuptools/issues/1684

https://github.com/pytest-dev/pytest/issues/5534

Fixes: #303
Change-Id: I345fd46f8911a71c039adf2d51937175142db793