caps: drop a non-surprising error report

Commit 60dd97a84 changed getVdsCaps to report whether we support live
snapshots. Usually, not having the relevant architecture in libvirt's
capapbilities is indeed a bug. However, this is not the case when we are
faking kvm support.

Change-Id: I5e8da158314420898935691e05db4591aa9176ec
Signed-off-by: Dan Kenigsberg <danken@redhat.com>
Reviewed-on: http://gerrit.ovirt.org/27704
Reviewed-by: Francesco Romani <fromani@redhat.com>
Reviewed-by: Antoni Segura Puimedon <asegurap@redhat.com>
Reviewed-by: Vinzenz Feenstra <vfeenstr@redhat.com>