vault/api/sys_health.go returns nil as a body when HTTP code is 429

[ghost]

We are checking each of our deployed vaults to determine if the vault is sealed or unsealed.
We are encountering a problem with the health check response in the client.

eg. health, err = v.Client.Sys().Health()

r := c.c.NewRequest("GET", "/v1/sys/health")
	resp, err := c.c.RawRequest(r)
	if err != nil {
		return nil, err
	}

When called for a vault pod which is a standby, the http response code 429 is correctly returned to indicate a standby instance, but the HealthResponse is discarded and nil is returned alongside, so we can never tell what state the vault is in !

Compared against a curl of the REST API

curl -v http://localhost:8200/v1/sys/health
*   Trying 127.0.0.1...
* Connected to localhost (127.0.0.1) port 8200 (#0)
> GET /v1/sys/health HTTP/1.1
> Host: localhost:8200
> User-Agent: curl/7.43.0
> Accept: */*
> 
< HTTP/1.1 429 Too Many Requests
< Cache-Control: no-store
< Content-Type: application/json
< Date: Thu, 08 Jun 2017 14:44:32 GMT
< Content-Length: 190
< 
{"initialized":true,"sealed":false,"standby":true,"server_time_utc":1496933072,"version":"0.7.0","cluster_name":"vault-cluster-7c947708","cluster_id":"dbf06f1f-6b8e-e900-4e44-895674d9f6f4"}

which returns information about the standby instance as well as the 429.