Console is not passing elasticsearch.customHeaders

[tbragin]

Kibana version:
5.0.0 (GA)
Elasticsearch version:
5.0.0 (GA)
Server/Browser OS version:
MacOS
Browser version:
Version 54.0.2840.71 (64-bit)
Original install method (e.g. download page, yum, from source, etc.):
Manual

Description of the problem including expected versus actual behavior:
As description says, Console is not passing elasticsearch.customHeaders

Steps to reproduce:

1. Add to kibana.yml:

elasticsearch.customHeaders: {x-found-cluster: fe65b96aaaff40608afce2ffbeb59f6b, x-cloud-cluster: fe65b96aaaff40608afce2ffbeb59f6b}

2. Create nginx proxy to Elasticsearch that logs the headers:

worker_processes  1;
daemon off;

events {
    worker_connections  1024;
}

http {
  include       mime.types;
  default_type  application/octet-stream;

  log_format  main  '$remote_addr - $remote_user [$time_local] "$request" '
                    '$status $body_bytes_sent "$http_referer" '
                    '"$http_user_agent" "$http_x_forwarded_for"'
                    '"$http_x_found_cluster" "$http_x_cloud_cluster"';

  access_log  /dev/stdout  main;

  sendfile        on;
  keepalive_timeout  65;

  server {
    listen 9229;

    access_log  logs/es-proxy.access.log  main;

    location / {
      proxy_pass http://localhost:9200;
    }
  }
}

3. Set elasticsearch.url in kibana.yml to http://localhost:9229
4. Use the Console App to query the stats API GET _stats and observe es-proxy.access.log:

$ tail -f /es-proxy.access.log | grep _stats
127.0.0.1 - elastic [02/Nov/2016:04:39:52 -0700] "GET /_stats HTTP/1.1" 200 157505 "-" "-" "127.0.0.1""-" "-"

Errors in browser console (if relevant):

Provide logs and/or server output (if relevant):

Describe the feature: