Adding the Django Discovery TestRunner #17365

This pull request adds the unittest2 test discovery to Django while specifying location for look up in `settings.py`

That being said, I have only updated the 1.5.txt release until the code is reviewed. Once that is complete I will update the testing documentation and what other documentation that needs to be updated as per discussion had here. 

Also let me know if I can improve the testing. I think I have tested the discovery test runner well but if it can be improved to cover edge cases let me know. 

Many thanks to @freakboy3742 for his guidance. 

https://code.djangoproject.com/ticket/17365 is the attached ticket