improve gnome-boxes diagnostics
Gnome boxes diagnostics should be made more verbose to help people debug their problems. Are diagnostics logged? If yes, where? Case in point: I kept trying to install some OS but it failed in the middle and all I got is a message "...has been automatically deleted." For reasons I can't follow, this message disappears after a few seconds. So it was only by luck that I discovered it. Also, I suggest to include the very useful output of gnome-boxes --checks somewhere in the GUI. (For the record: I'm using Gnome-boxes 3.30.3 from Debian/buster.)