illumos gate

I have discovered two issues with the libbrand dtd's:

1: forcedlogin_cmd is optional but the dtd marks it as required.
2: arch and ip-type both default to "all" but all is not marked as an acceptable value.

Previously this would not have been a problem but libbrand now validates it's xml files making these BrandZ zones unusable with Illumos. The attached patch address these issues.