kiwi build script uses package.onlyarch, which does not exist anymore

[Vogtinator]

The kiwi build script does

if ($package->{'onlyarch'} && $package->{'onlyarch'} eq "skipit") {

which does not work anymore as packages now have an arch attribute and onlyarch is not allowed.

Workaround: <package name="aaa_base" replaces="ignored package"/>

[Vogtinator]

OBS needs to handle <ignore name="foo"> as well.