Add the graphical upgrade tests.
    
    This PR builds on some elements of the current upgrade process,
    such as upgrade_boot, upgrade_preinstall, upgrade_postinstall, but
    replaces the upgrade_run with graphical_upgrade_run to use graphical
    methods to upgrade the system.
    This would not be possible without necessary settings, that are
    performed by graphical_upgrade_prerequisites.
    Works for both Gnome and KDE.