The existing run_tests.py script is quite old (un-maintained?) and
doesn't always always behave documented.

The pytest testing tool has been around for quite a while, it is mature,
well documented, maintained and used by a large number of other python
projects.

I am proposing that we replace the existing run_tests.py script with a
pytest standalone script.

A proposed patch set will be attached shortly. Though you can also view
the changes in the 'pytest' branch on my github clone:

  https://github.com/jerrykan/roundup/commits/pytest