PR#1434: hub: fix check_fields and duplicated parent_id in _writeInheritanceData
    
    Merges #1434
    https://pagure.io/koji/pull-request/1434
    
    Fixes: #1435
    https://pagure.io/koji/issue/1435
    changes for writeInheritanceData should not contain duplicated parent_id
    
    Fixes: #1433
    https://pagure.io/koji/issue/1433
    writeInheritanceData checks wrong field for "delete link"