PR#2649: kojid: backward compatible hub call
    
    Merges #2649
    https://pagure.io/koji/pull-request/2649
    
    Fixes: #2648
    https://pagure.io/koji/issue/2648
    kojid 1.23 does not cope with kojihub 1.21 (  ParameterError: getAverageBuildDuration() got an unexpected keyword argument 'age')