Elasticsearch stats URL doesn't return certain stats

[threetee]

When using elasticsearch version 0.19.9, the default elasticsearch stats URL that the plugin queries doesn't provide stats for http, process, jvm, and transport, so the plugin fails with the following error:

Sep  3 16:37:14 localhost collectd[16116]: Unhandled python exception in read callback: TypeError: int() argument must be a string or a number, not 'NoneType'
Sep  3 16:37:14 localhost collectd[16116]: read-function of plugin `python.elasticsearch' failed. Will suspend it for 40 seconds.

I've already fixed this in my fork, so I'll send a pull request.