Thanks for coming back with the actual cause instead of leaving it hanging.
To me, a permissions reset on /etc/rc.d/rc.local would explain it completely, and it fails in the worst way, since nothing complains at boot and the VMs just never start.
It also looks worth documenting, because our own troubleshooting page tells people to append a clocksource workaround to /etc/rc.local without mentioning the executable bit either, so anyone following that could end up with a workaround that quietly does nothing.
I haven't tested whether the 8.2 to 8.3 upgrade resets that bit every time or just happened to in your case, so that half stays your finding, not mine.
I'm curious what you turn up on the colon versus equals behaviour.
