[libvirt] Hyervisor Features elements

[bancfc at openmailbox.org]

Hello. Under Hypevisor Features for Domain elements, I noticed new 
features being added like

<kvm>
   <hidden state='on'/>
</kvm>

Probably more will be added later I am guessing.

-Is this a performance feature?
-Can it also be applied to qemu only machine templates? (I don't use 
qemu only, but maintain templates for both that's the reason for asking)