improve logging for longevity tests
refactor EntityCleanupLongevityTest so that (1) it checks explicitly that things have been cleaned up, (2) we have a unit test as well as a long-running test, and (3) the long-running test makes memory assertions; currently explicitly excuses certain leaks (which we want to patch soon)
reply to code review comments, method now called `isMostlyEmpty`
Merge pull request #1305 from ahgittin/improve-cleanup-testing

Improve cleanup testing