[branch] install-media defaults to stable branch
Created by: manjaro
Sure we use branches on creating our images, but is it wanted to default on stable rather than the branch we build our install-media on? We might call this after root-image creation:
cp "${PKGDATADIR}/pacman-mirrors-${branch}.conf" "${work_dir}/root-image/etc/pacman-mirrors.conf"
Otherwise we can add another switch if other options are wanted ...