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?
Let's use a more descriptive name.  The output is 2 columns, `Variable_name` and `Value`, so how about `varName`?