Major Description
HistoryServer has 2 formats. The old one makes a directory and puts multiple files in there (APPLICATION_COMPLETE, EVENT_LOG1 etc.). The new one has just 1 file called local_2593759238651.log or something.
It's been a nightmare to maintain both code paths. We should just remove the old legacy format (which has been out of use for many versions now) when we still have the chance.
