Use /run instead of /var/run as ROOT

Chromium OS ToT now uses `/run` in anticipation of a udev uprev, with `/var/run` being a symlink for compatibility. `fixabslinks` assumes no symlink in the `CHROOT` variable, so `/run` should be used directly when passing paths to fixabslinks.

Otherwise, `fixabslinks` will get stuck in an infinite loop in `enter-chroot`.