Under compaction mark may leak

HBASE-26249 introduced an under compaction mark to reduce repeatedly compactions for the same stores for a short period of time after bulk loading files.

Since the mark adding and removing are in difference threads,

pool.execute(
  new CompactionRunner(store, region, compaction, tracker, completeTracker, pool, user));
if (LOG.isDebugEnabled()) {
  LOG.debug(
    "Add compact mark for store {}, priority={}, current under compaction "
      + "store size is {}",
    getStoreNameForUnderCompaction(store), priority, underCompactionStores.size());
}
underCompactionStores.add(getStoreNameForUnderCompaction(store)); 

 it happens that the concurrently of thread-1 using underCompactionStores.add() and thread-2 which running a CompactionRunner that using underCompactionStores.remove(). If the removing happens before adding, the mark will leak.