The pungi-config-validate --dump-schema now respects --schema-override.
    
    It is useful to actually check how the schema changed after applying
    --schema-override. This commit changes --dump-schema in a way that
    --schema-override is taken into account and dumped schema contains
    the changes done using the --schema-override.
    
    Signed-off-by: Jan Kaluza <jkaluza@redhat.com>