Comment 19 for bug 1716028

Umm, the latter is the official way to go, but only in latter libvirt versions.
https://libvirt.org/git/?p=libvirt.git;a=commit;h=28907b0043fbf71085a798372ab9c816ba043b93

I'm adding a libvirt bug task for the bionic merge to pick that up "explicitly"