Checking for updates failed when MaintenanceTool printed out log
messages. MaintenanceTool is expected to print out only xml data. So,
parsing the output failed.

MaintenanceTool printed out warnings about SSL and Qt account.

Logging is now disabled when running MaintenanceTool.

Change-Id: Ib163dae81368c8fec7218e5961590e07c208a73e
Reviewed-by: Eike Ziller <eike.ziller@qt.io>