After a secure bulkload finished , there is a clean-up for FileSystems used in the bulkload.
Sometimes, FileSystems used in the finished bulkload might also be used in other bulkload
calls, or there are other FileSystems created by the same user, they could be closed by a
FileSystem.closeAllForUGI call. So during the clean-up, those FileSystems need to be used
later can not get closed ,or else a race condition occurs.
testForRaceCondition tests the case that two secure bulkload calls from the same UGI go
into two different regions and one bulkload finishes earlier when the other bulkload still
needs its FileSystems, checks that both bulkloads succeed.