[poky] RFC: add new init system alternative to poky

[Niko Mauno]

To whom it may concern;

attached patches (which work for me on top of Poky commit
b76161a9a890481e8418a34b3250fc2debcb566f) serve by adding initial
support for an alternative modern init system called OpenRC to
Yocto-generated Linux OS distributions.

https://wiki.gentoo.org/wiki/OpenRC
https://wiki.gentoo.org/wiki/Comparison_of_init_systems

Motivation: Systemd may not suit everyone, but SysVinit is also very
old and unmaintained. OpenRC provides modern init features, such as
parallel service startup and automatic restarting of crashed services,
while retaining an Unix-like approach of doing things.

While relying on SysVinit's /sbin/init, the OpenRC documentation page
claims that BusyBox-provided init program is also supported at least
to some extent currently.

While developing I've tested against the poky master branch's
core-image-full-cmdline, which boots and halts for me seemingly
without errors.

With following openrc_%.bbappend:
  do_install_append() {
    echo 'keymap="fi"' >> ${D}${sysconfdir}/conf.d/keymaps
    echo 'rc_logger="YES"' >> ${D}${sysconfdir}/rc.conf
  }
I got the console keymap working for me, and a boot log at
/var/log/rc.log, like which Yocto's sysvinit has so far provided.

The second patch which modifies openssh recipe, is a sample showing
how to add openrc support to existing recipes. The OpenRC specific
conf, init files are readily available from Gentoo project, so there
shouldn't be any need to come up with those files from scratch. With
the openssh patch, I'm able to login in to core-image-full-cmdline
(executed via runqemu qemux86) via ssh right after the image OS has
booted.