[archiso] Set default SquashFS compressor to XZ
[archiso] Set default SquashFS compressor to XZ

Also change all references from lzma to xz format.

Signed-off-by: Gerardo Exequiel Pozzi <f366e24919a755584052c42c8303af2b142d3e55@yahoo.com.ar>

dock0/dock0