pwpolicy-mod doesn't accept old attribute values
    
    When the pwpolicy attribute "cospriority" is passed to pwpolicy-mod
    command and the old value is kept, the command should succeed
    if there was at least one other attribute changed. Current
    pwpolicy-mod raises exception in this case which may lead to issues
    in the WebUI.
    
    https://fedorahosted.org/freeipa/ticket/1104