Explicitly call "/etc/rc.d/vmd stop". This issues graceful shutdown commands

Explicitly call "/etc/rc.d/vmd stop". This issues graceful shutdown commands
to running VMs (at least for OpenBSD ones), but the stop routine for system
daemons is not usually called at shutdown.

Earlier version with just "vmd stop" ok reyk@ kn@, ajacoutot@ reminded me
to hide the contextless "vmd(ok)" text which looks bad, I did so and wrapped
it with a "stopping VMs" message (it can take some time, especially when you
have multiple VMs, so better to have some clear feedback).