Use replace instead of add to set new default ipaSELinuxUserMapOrder
    
    The add was in effect replacing whatever data was already there
    causing any custom order to be lost on each run of
    ipa-server-upgrade.
    
    https://pagure.io/freeipa/issue/6610
    
    Signed-off-by: Rob Crittenden <rcritten@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>
    Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>