investigate how test discovery and module import should be used for integration test

[thinkingfish]

A few questions here:

• should we use python3? There's no historical baggage, so the question boils down to if there are new features that would benefit testing.
• what's the best way to do test discovery? We use unittest.TestCase a little differently from how it is normally done (by loading from a list of files to create individual TestCase's instead of specifying the entire test in-place), so we may or may not be able to use the standard unittest discovery mechanism.
• what's the best way to import modules? Mostly just not familiar with how python2/3 differ on this aspect.

[thinkingfish]

We should use py3 from this point on.