QtIFW

Fixes QTIFW-35.

Can't close the maintenance tool while the details widget is
shown during perform update or installation. We need to check
if the core engines state is already canceled and than we can
close the whole application.

Change-Id: I332e7fcc4f9012fdf5ed84d23cf09cb1479ca72f
Reviewed-on: http://codereview.qt-project.org/4474
Reviewed-by: Qt Sanity Bot <qt_sanity_bot@ovi.com>
Reviewed-by: Tim Jenssen <tim.jenssen@nokia.com>
Reviewed-by: Karsten Heimrich <karsten.heimrich@nokia.com>