When a hidden service sets up its circuits, it uses `rend_service_requires_uptime()` to check the type of service it's setting up, and if it's setting up a long-lived service (e.g. SSH, etc.) it will only use Stable nodes for its rendezvous circuits. We should consider if this is a good idea wrt security, and potentially kill this feature if we think it restricts our path selection too much or reveals too much info to the RPs.