Fix div-by-zero when svc weight is 0 for all masters in location
    
    The relative service weight output tries to show the relative
    chance that any given master in a locaiton will be picked. This
    didn't account for all masters having a weight of 0 which would
    result in a divide-by-zero error.
    
    Implement the following rules:
    1. If all masters have weight == 0 then all are equally
       weighted.
    2. If any masters have weight == 0 then they have an
       extremely small chance of being chosen, percentage is
       0.1.
    3. Otherwise it's percentage change is based on the sum of
       the weights of non-zero masters.
    
    https://pagure.io/freeipa/issue/8135
    
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>