Make `status` endpoint to don't return 503 error code

[davidyuk]

$ curl -D - https://mainnet.aeternal.io/middleware/status
HTTP/1.1 503 Service Unavailable
Date: Mon, 30 Dec 2019 06:56:34 GMT
Server: Rocket
content-type: application/json
Content-Length: 110
Access-Control-Allow-Origin: *
Connection: close

{"OK":false,"errors_last_500_blocks":0,"queue_length":47,"seconds_since_last_block":144304,"version":"0.13.0"}

Returning of the 503 error with the correct response looks confusing. We are using axios to get status, and it fails with an exception, but in this case, we can handle the response as usual. I think the status endpoint should return error code only if it can't return the response with the usual structure.

[johnsnewby]

We rely on this behaviour.

[davidyuk]

Can you elaborate?