schema: Eliminate 'class' from StorageDomainInfo

'class' is usually a reserved word and makes a bad name for a type field.
Change it to domainClass and add the required type fixup to the Bridge.

Change-Id: I7d13d4c6141e42c996b50a86d4b812c8c42f831f
Signed-off-by: Adam Litke <agl@us.ibm.com>
Reviewed-on: http://gerrit.ovirt.org/11711
Reviewed-by: Saggi Mizrahi <smizrahi@redhat.com>