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?
I think this should return a `mock.MySQLConnection` (which implements the `Connector` interface).  We probably need to 2 mock factories: one for returning null clients, another for returning mock MySQL clients.