Not all databases are cleaned up after an integration test run

[olavloite]

Databases that are created during an integration test run are not all deleted. This causes RESOURCE_EXHAUSTED errors to pop up in the builds after a while, and the databases need to be manually deleted before getting the builds green again. We should:

1. Check all integration tests for any databases that are created, but not deleted afterwards.
2. Implement an automatic clean-up job at the start of each integration test run that scans for test databases with a known name format, and then delete the databases that are older than X time.