schema: fix param default value handling
    
    Advertise param's default value even when `autofill` is False. When
    `autofill` is False, set `alwaysask` to True in the schema, as it is
    semantically equivallent and removes redundancy.
    
    This fixes default value disappearing in CLI for some params.
    
    https://fedorahosted.org/freeipa/ticket/4739
    
    Reviewed-By: David Kupka <dkupka@redhat.com>