Make node /health endpoint compatible with Consul health check

[edgarasg]

https://www.consul.io/docs/discovery/checks#http-interval

The basic idea is to return such HTTP status codes conditionally:

• 200 if bootstrapped: true
• 429 if bootstrapped: false
• 500 if status: down

This would be handy for automated rolling upgrade procedure.

[edgarasg]

If we agree on this change, I can make a PR.

[edgarasg]

Browsing through the code I've found /bootstrapped, so closing this.