Allocate storage to pure live media
Allocate storage to pure live media

We use qcow2 so it doesn't really matter if storage goes unused but we
should do this just in case our knowledge/assumption about inavailability
of installer is wrong.

https://bugzilla.gnome.org/show_bug.cgi?id=665254

vbenes/gnome-boxes,vbenes/gnome-boxes