schema: Decrease schema TTL to one hour
    
    Since checking schema is relatively cheap operation (one round-trip with
    almost no data) we can do it offten to ensure schema will fetched by
    client ASAP after it was updated on server.
    
    https://fedorahosted.org/freeipa/ticket/4739
    
    Reviewed-By: Petr Spacek <pspacek@redhat.com>