[arch-releng] Squashfs

[Mr Green]

Currently to convert root-image to a real install we unsquash 
root-image.fs.sfs then mount root-image.fs then copy from there.

We have already got image mounted
/dev/loop0 on /run/archiso/sfs/root-image type squashfs (ro,relatime)

Trying to take out an unsquash action to reduce install time, it will 
only work if I can mount

/run/archiso/sfs/root-image/root-image.fs

Have feeling I am not going to be able to mount it twice.

MrG