This fixes reverting to snapshots created by older libvirt
and allows libvirt not to lose track of a domain that
has this in its live status XML (such as a domain
restored from managedsave)

https://bugzilla.redhat.com/show_bug.cgi?id=1030793
https://bugzilla.redhat.com/show_bug.cgi?id=1151885
(cherry picked from commit 15abebde)