When the files we're creating in the live layer have static content, ship
them in live-build/ubuntu/includes.chroot.minimal.standard.live instead of
generating them from live-build/ubuntu/hooks/020-ubuntu-live.chroot_early.
Also fixes the fact that
live-build/ubuntu/hooks/020-ubuntu-live.chroot_early was incorrectly writing
to /root in the previous upload instead of /usr.