Less (SLOC) is more

Update the monitoring-vpn changes in here so reading the changes is less awkward

... so Grafana shows us names instead of VPN IP addresses.

Avoiding catastrophy: It's all about minimizing cognitive overhead.

We have enough numbers with little value already

Make everything more consistent and generally more nice.
I am a bit proud of this now.
Let's hope it holds up.

Rationale: These are servers, they should be transmitting mostly.
But really it's rather arbitrary.

- Add node exporter to nodes
- Make the old nixpkgs 19.09 node exporter work (amend config)
- Fix a typo (??) and exclude monitoringvpn in network traffic graphs to prevent double counting

... and make path an option.

  sed -i 's|var/secrets|run/keys|'

See Ops#193

Get the local dev env running: Add keys

See merge request !83