The following is expected to raise an error:
<os>
<loader readonly='yes' type='pflash'/>
</os>
because no path to the pflash loader is given and there is
no default built-in.
Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>
