systemd host: wait for guests shutdown before host restart/poweroff

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Hi all
I am running virtualbox 5.2.6 in Ubuntu 16.04.3
I have configured VMs (actually only one) guest to autostart and autostop by using vboxautostart-service
The main command:

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VBoxManage modifyvm <vmname> --autostart-enabled on

and for poweroff I have selected acpishutdown, that normally works if triggered by GUI (or actually by phpVirtualbox) and command line

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VBoxManage modifyvm <vmname> --autostop-type acpishutdown

The VM perfectly startup automatically at the host power up, but the host shutdown I think it is too fast and I don't have evidence that it actually waits for guest shutdown
Is vboxautostart-service expected to manage the guest-host shutdown sequence? Ho can I check it?
Thanks, bye