PCT-637: Query Analytics does not handle MySQL Restart

Done

However, I'm afraid that FileIntervalIter goroutine might access mysqlConn.Connect/Close/Set at the same time as the goroutine with check if mysql was restarted. @daniel-nichter What you think? Should I protect mysql.Connection with mutex?
Btw, I'm saying MySQL is in fact restarted but agent can't connect for awhile.  In your comment, you said "server was not restarted and this is correct" but the hypothetical here is that MySQL was restarted.  So yes, current code works in normal case (restart without problem) but not in case of restart with problem.