Feature: DatabaseJanitor Isolation Level

[jcpunk]

What action do you want to perform

It appears that the isolation_level is hard coded to ISOLATION_LEVEL_AUTOCOMMIT. It would be handy if I could alter that for both the DatabaseJanitor class and the postgresql fixture.

What are the results

The database tests with a specific isolation level. My approved database config uses a different isolation level. As a result, my tests are technically different than what I'm running in production.

What are the expected results

A way to tweak the isolation for folks (like myself) with strange requirements.

[1] https://github.com/ClearcodeHQ/pytest-postgresql/blob/master/src/pytest_postgresql/janitor.py#L82