qemu: Simplify handling of virTristateBool values
qemu: Simplify handling of virTristateBool values

We explicitly check whether the value is YES or NO, which makes
it unnecessary to make sure it's not ABSENT beforehand.

Signed-off-by: Andrea Bolognani <3ada0bee826c753786fdbba72243dfba997094cf@redhat.com>
Reviewed-by: Ján Tomko <4cab11cfb98d3c937327354a78eb07dbb6ee2bc6@redhat.com>

zippy2/libvirt,zippy2/libvirt,jfehlig/libvirt,zippy2/libvirt,olafhering/libvirt,libvirt/libvirt,jfehlig/libvirt,libvirt/libvirt,jfehlig/libvirt,libvirt/libvirt,olafhering/libvirt,crobinso/libvirt,jfehlig/libvirt,crobinso/libvirt,libvirt/libvirt,crobinso/libvirt,zippy2/libvirt,olafhering/libvirt,olafhering/libvirt,crobinso/libvirt