This allows to run a service but do not cause a qube to be started it
isn't already running. This is especially useful for background /
internal calls designed to service a running target VM - if VM is not
running, those do not make sense to be called in the first place.
Specifically, this will allow qvm-start-gui to avoid re-starting a
domain while calling qubes.NotifyMonitorLayout, when a VM is shutdown
shortly after its startup.
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