qemu: don't check for backing chains for formats w/o snapshot support
qemu: don't check for backing chains for formats w/o snapshot support

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=1019926
Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=868673

Signed-off-by: Martin Kletzander <e82f23e74d43760279ebcc505dac4ae70d5627d0@redhat.com>

taget/libvirt,eskultety/libvirt,olafhering/libvirt,zippy2/libvirt,fabianfreyer/libvirt,zippy2/libvirt,shugaoye/libvirt,eskultety/libvirt,rlaager/libvirt,crobinso/libvirt,andreabolognani/libvirt,datto/libvirt,nertpinx/libvirt,VenkatDatta/libvirt,datto/libvirt,nertpinx/libvirt,agx/libvirt,elmarco/libvirt,crobinso/libvirt,fabianfreyer/libvirt,elmarco/libvirt,nertpinx/libvirt,shugaoye/libvirt,zippy2/libvirt,jfehlig/libvirt,libvirt/libvirt,VenkatDatta/libvirt,taget/libvirt,eskultety/libvirt,fabianfreyer/libvirt,datto/libvirt,jardasgit/libvirt,eskultety/libvirt,andreabolognani/libvirt,taget/libvirt,jardasgit/libvirt,olafhering/libvirt,VenkatDatta/libvirt,elmarco/libvirt,elmarco/libvirt,libvirt/libvirt,crobinso/libvirt,agx/libvirt,agx/libvirt,jfehlig/libvirt,nertpinx/libvirt,olafhering/libvirt,andreabolognani/libvirt,taget/libvirt,olafhering/libvirt,agx/libvirt,jfehlig/libvirt,libvirt/libvirt,rlaager/libvirt,jardasgit/libvirt,shugaoye/libvirt,jardasgit/libvirt,rlaager/libvirt,jardasgit/libvirt,andreabolognani/libvirt,shugaoye/libvirt,taget/libvirt,fabianfreyer/libvirt,jfehlig/libvirt,VenkatDatta/libvirt,rlaager/libvirt,crobinso/libvirt,fabianfreyer/libvirt,rlaager/libvirt,libvirt/libvirt,agx/libvirt,elmarco/libvirt,datto/libvirt,shugaoye/libvirt,andreabolognani/libvirt,VenkatDatta/libvirt,nertpinx/libvirt,zippy2/libvirt,datto/libvirt,eskultety/libvirt