Clear out tables after end-to-end tests

At the moment we're only clearing out `faces` and the Rekognition database. While this should cause clashes in subsequent testing runs due to uuid use, it makes tests more expensive over time, and harder to diagnose.

Ideally this should track the *created* items and only delete those at the end of a run, so we can run end-to-end tests concurrently from local and CI environments without causing mystery bugs.