Docker files for elasticsearch stack.

TODO:
- [x] Don't use `root`.
- [ ] Enable automatic builds in clusterhq organization. (I have ones for test at https://hub.docker.com/u/tomprince/)
- [x] Document the images.

```yaml
"version": 1
"applications":
  "elasticsearch":
    "image": "tomprince/test-elasticsearch"
    "ports":
    - "internal": 9200
      "external": 9200
    "volume":
      "mountpoint": "/var/lib/elasticsearch/"
  "logstash":
    "image": "tomprince/test-logstash"
    "ports":
    - "internal": 5000
      "external": 5000
    "links":
    - "local_port": 9200
      "remote_port": 9200
      "alias": "es"
  "kibana":
    "image": "tomprince/test-kibana"
    "ports":
    - "internal": 8080
      "external": 80
```