That was a major pain.
* deleting a topic & contents takes ~2s locally, tripled test time when
  run after every test
* Kafka consumer polling is pretty slow, and can't be done mid test if
  assert _close_to_now is used.
* It seems as though not closing clients can cause weird errors/hangs in
  other clients? Not 100% sure about this, was making too many changes
  too rapidly trying to figure out what was going on. Closing doesn't seem
  to hurt  though.

also flake8 mysteriously started whining about new stuff even though it
wasn't updated.