avro

AVRO-3033: Fix flaky file descriptor test (#1078)

It looks like before fixing the bug AVRO-2286, the number of openFilesBeforeOperation was always greater than openFilesAfterOperation. In practice, now they're usually the same value, which is promising evidence that there isn't a resource leak there.

The flakiness of the test comes from the fact that "something" might be fuzzing either of them off by one. I used to see this in travis and local builds too (but infrequently). It might be a background, system-process or an action like garbage collection. I don't think it's instability of the machine, it's just not as deterministic as we'd like.