ensure lists/ files have correct permissions after apt-cdrom add

ensure lists/ files have correct permissions after apt-cdrom add

Its a bit unpredictable which permissons and owners we will encounter on
a CD-ROM (or a USB stick, as apt-cdrom is responsible for those too),
so we have to ensure in this codepath as well that everything is nicely
setup without waiting for a 'apt-get update' to fix up the (potential)
mess.