Add sys-apps/openrc

This is fake OpenRC package, which only provides /etc/init.d/functions.sh needed for some packages

See https://bugs.gentoo.org/show_bug.cgi?id=373219#c40
openrc: add dependency on virtual/init
openrc: remove setup_defaultlevels
openrc: replace functions.sh

This is a cleaner version of funstions.sh, which closely matches that of the OpenRC