Switch default authentication to `local`
    
    Most setups aren't going to have any of the other methods available
    by default, and if they want to use it, it's easy enough to configure
    otherwise.
    
    Merges https://pagure.io/pagure/pull-request/3270
    
    Signed-off-by: Neal Gompa <ngompa13@gmail.com>
    Signed-off-by: Pierre-Yves Chibon <pingou@pingoured.fr>