rules: clean up stale CD drive mounts after ejection

Ejecting a CD with the hardware drive button only causes a change uevent, but
the device node stays around (just without a medium). Pick up these uevents and
mark the device as SYSTEMD_READY=0 on ejection, so that systemd stops the
device unit and consequently all mount units on it.

On media insertion, mark the device as SYSTEMD_READY=1 again.

https://bugs.freedesktop.org/show_bug.cgi?id=72206
https://bugzilla.opensuse.org/show_bug.cgi?id=909418
https://bugs.archlinux.org/task/42071
https://bugs.launchpad.net/bugs/1168742