Add dynamic $tty to finish.agetty script too

Whoops.
Change install paths for sys-process/runit

This upgrade is intentionally awkward and requires manual intervention, because
it has the potential to brick your system if you don't pay attention.

It's straightforward enough; just move your runsvdir/all stuff to /etc/sv/, your
runsvdir/default symlinks to /etc/service/, then reboot when you're ready.