Include the hostname in graphite metrics

This is a fix for #19. Example graphite metrics...

```
discodns.Toms-MacBook-Pro-2_local.request.handler.tcp.response_time.50-percentile 0.00 1406848500
discodns.Toms-MacBook-Pro-2_local.request.handler.tcp.response_time.75-percentile 0.00 1406848500
discodns.Toms-MacBook-Pro-2_local.request.handler.tcp.response_time.95-percentile 0.00 1406848500
discodns.Toms-MacBook-Pro-2_local.request.handler.tcp.response_time.99-percentile 0.00 1406848500
discodns.Toms-MacBook-Pro-2_local.request.handler.tcp.response_time.999-percentile 0.00 1406848500
```