Use tags for datadog metrics

 :sparkles: :fire: :clap: :sparkles: => DataDogTags

/cc @Shopify/data-engineers 

![screen shot 2014-03-11 at 14 53 19](https://f.cloud.github.com/assets/48745/2389571/9045e55c-a94f-11e3-9990-34ccc852a4c7.png)

unfortunately, all the worker and master stuff needs to be tested on the cluster (or some cluster). so, no warranties given... :trollface: