Comment 2 for bug 1497449

Because of repeated failed attempts to create USB devices, eventually usb-creator-gtk will fail because of the lack of loop devices. If I forgot to unmount all the ISO and squashfs mounts after the failed attempts at USB creation (2 mounts per attempt), I run out of loop devices and the creator fails immediately because it's unable to create a new squashfs mount, or unable to mount any more ISOs.