Fix broken Dashboard/Prometheus export for relay01 host metrics and d2d4 host and unbound metrics

During the past days it seems a bunch of metrics vanished from our Grafana dashboards:

1. relay-01 host metrics
2. d2d4 host metrics
3. d2d4 unbound metrics

I poked a bit around but was not able to get things fixed immediately, hence this ticket. /cc @dgoulet

It's a bit weird that relay-01 metrics host metrics is affected as well as this is a TPA managed machine. /cc @hiro for that part.