metadata/layout.conf: set explicitely master repo as gentoo
tree57dbd4552f6d0eebf395b59cdf502ac6c1ec41aa
drwxr-xr-x - app-portage
drwxr-xr-x - dev-lang
drwxr-xr-x - dev-ml
drwxr-xr-x - dev-util
drwxr-xr-x - dev-vcs
drwxr-xr-x - games-arcade
drwxr-xr-x - media-sound
drwxr-xr-x - metadata
drwxr-xr-x - net-fs
drwxr-xr-x - net-libs
drwxr-xr-x - net-p2p
drwxr-xr-x - profiles
drwxr-xr-x - sys-fs