separate workers for meta table is not working

This is an addendum for HBASE-21423, since HBASE-21423 is already closed, the QA won't be triggered.
It is my mistake that the separate workers for meta table is not working, since when polling from queue, the onlyUrgent flag is not passed in.
And for some UT that only require one worker thread, urgent workers should set to 0 to ensure there is one worker at time.