qemu: propagate virDomainJobObj into qemuDomainObjPreserveJob()
It does not make sense to propagate virDomainObj and get
qemuDomainObjPrivate from it, when it is already accessible in
the only function qemuDomainObjPreserveJob() is called from. That
being said, we can also propagate virDomainJobObj directly and
avoid using qemu private structure.
Signed-off-by: Kristina Hanicova <khanicov@redhat.com> Reviewed-by: Michal Privoznik <mprivozn@redhat.com>