Clean up DB migrations when running unit tests

When doing development work, all kinds of issue can result when moving
between versions of the code that have added/removed DB migration scripts
if the compiled .pyc files are left behind. To save the need to do this
manually, remove all of the .pyc files when the unit tests are run.

Change-Id: Ia4bc889edeeed499e5fc2172d5f7c1b4e693a27b
Merge "Clean up DB migrations when running unit tests"