Use only AES enctypes by default
    
    Remove des3 and arcfour from the defaults for new installs.
    
    NOTE: the ipasam/dcerpc code sill uses arcfour
    
    Signed-off-by: Simo Sorce <simo@redhat.com>
    
    Ticket: https://fedorahosted.org/freeipa/ticket/4740
    Reviewed-By: Martin Basti <mbasti@redhat.com>
    Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>