OPENRC: simplify service, fix bug on shutdown

/etc/init.d/swapfiles unmounts all tmpfs and eventually does so
before psd service is stopped resulting in a broken symlink
and no resync.
use /etc/psd.conf for gentoo, simplify initscript
remove openrc specific cron script

the regular one just works fine
OPENRC: remove obsolete override
fix installing openrc and systemd together
Merge pull request #47 from gentoo/master

Fix https://bugs.gentoo.org/show_bug.cgi?id=398431