This commit just moves all the unmodified files into their new
locations. The interesting changes are in the next commit.

Signed-off-by: James Le Cuirot <jlecuirot@microsoft.com>

Catalyst 4 has totally changed the way repositories are handled. It only
works when the name of the directory containing the repository matches
the configured name of that repository. We already renamed coreos to
coreos-overlay accordingly, but we actually want entirely different
names and more convenient locations too.

The repositories are now known as gentoo-subset and flatcar-overlay, and
they live under scripts/repos. Using the same name as upstream Gentoo
would have been problematic, and just "flatcar" would have looked
awkward in documentation.

I have removed code referencing /mnt/host/source/config rather than fix
it up, as this is no location is no longer used anywhere.

Signed-off-by: James Le Cuirot <jlecuirot@microsoft.com>