The NBD drive mirror workaround requires this, also the new -IBRS
machine types, and EPYC cpu models are only available in the newer
qemu versions
Also ensures that we can now allow to hot-unplug virtio-scsi disk
with iothread active, as the fix for it is also in v2.9.1
(virtio-scsi: Unset hotplug handler when unrealize)