Monitor relays that are not measured by each sbws instance

If sbws isn't measuring a relay, either:

• the relay is misconfigured, or
• there is a bug in sbws (like #28519 (moved))

We should decide how long it should take sbws to measure a relay. Then we should create a list of the relays that aren't measured by sbws.

When we work out why a relay isn't being measured by sbws, we should contact the operator (or fix the bug).