[libvirt] libvirt-guests.sh without or with failing ACPI support

[Henning Schild]

Hi all,

the systemd shutdown scripts work sequentially with a 300s timeout
(seen on Debian). If a VM does not have ACPI support, or the ACPI
support failed for some reason, you are looking at a 300s timeout per
instance for a host shutdown/reboot.
i.e. 10 instances without working ACPI = 3000s to shut down

I think the systemd scripting should be parallel instead of
sequentially. So if you have many VMs without working ACPI you just
have to wait 300s in total for the host to shut down.

Steps to reproduce:
 - star a VM that does not support ACPI
 - reboot the host and wait 300s for the VM to be shut down
 - now start it multiple times
 - wait multiples of 300s for the shutdown

Expected behaviour:
 - no matter how many instances do not support ACPI, make it 300s max
   because we shut them down in parallel 


regards,
Henning