Cleanup tables after each test
Cleanup tables after each test

Closes https://github.com/Shopify/lhm/issues/46

This improves test isolation while also setting the stage to address
https://github.com/Shopify/lhm/issues/47 by shortening the timestamps
in "lhma" tables. Without this cleanup, and without the precision of those
timestamps, tests were failing reporting duplicate table names.

Shopify/lhm,Shopify/lhm