There are currently only power states "on/off" on the host detail page (independently of the the actual compute resource).

On the all host page you can select one or more hosts, click "Select Action" > "Change Power State" and choose from various power states like "start/stop/poweroff/reboot/reset/soft/cycle".

This is quite inconsistent in my eyes, why not allow toggling all desired power states also on host detail page?

Having this, libvirt VMs can then also be shut down consequently (=poweroff) if no OS is running (currently, power state "off" has no effect if no OS is running in VM).