guest-overlay: Always recreate squashfs without appending
Without -noappend, we end up with an image containing gast, gast_1,
gast_2 etc. after running repeatedly. This way, it is always recreated and
contains only what it is supposed to.
Without -noappend, we end up with an image containing gast, gast_1,
gast_2 etc. after running repeatedly. This way, it is always recreated and
contains only what it is supposed to.