Clean up integration tests

[mehaase]

At some point while writing tests, I decided to factor out database queries into the starbelly.db module. This allows me to write unit tests of other modules without a database dependency, and then the queries are covered by a series of integration tests. But I didn't have time to update modules/tests that I created before making this decision, such as test_robots.py, test_subscription, login.py, etc. Grep for db_pool—it should only appear in db.py—and refactor modules to not use it.

[mehaase]

Update: I removed test_robots.py while fixing a design flaw in bd25ddb. The robots manager still needs to be updated with a database abstraction layer.