Each boot, regenerate /var/run/os-release based on the currently running
system. Create a /etc/os-release symlink pointing to this file (so that this
doesn't create a new reason /etc can not be mounted read-only).
This is compatible with what other systems do and is what the sysutil/os-release
port attempted to do, but in an incomplete way. Linux, Solaris and DragonFly all
implement this natively as well. The complete standard can be found at
Moving this to the base solves both the non-standard location problem with the
port, as well as the lack of update of this file on system update.