add unit test for Port Alias table
Configure tox to discover and run tests

DHC-765
* create a django application to run tests
* configure tox.ini to use django tests runner
* pep8 clean up

Change-Id: I925cea7084512f1aca141a788256774f3f72c596
Merge pull request #63 from rodis/feature/port-alias-tests

Configure tox to discover and run tests