Adjust inspectdb management command to yield output following the Django Coding Style

With this change, the successful output of running the `inspectdb` command complies with style guidelines set forth in /docs/internals/contributing/writing-code/coding-style.txt. While that document refers to the best practices when coding for The Django Project, and not a developer's own project, I feel that consistency with internal practices is good.

I've added a test that checks for this behavior using the 3rd-party _pep8_ Python library (included).