contrib/openrc/init.d/package-cache: Nest more deeply

Gentoo's doinitd can't handle renaming the files it installs, so
create a deeper tree where the init script can be called
'package-cache'.  This layout leaves room for a future
contrib/openrc/conf.d/package-cache if we want to supply one.

diff --git a/contrib/openrc-init b/contrib/openrc/init.d/package-cache
similarity index 100%
rename from contrib/openrc-init
rename to contrib/openrc/init.d/package-cache