Add report-hostname to statsd settings.

Hey guys,

We were thinking that it would be nice if we can have a way to control whether  the hostname is reported to statsd or not. We added some specs and tested locally :) 

What do you guys think? 
Probably `include-hostname` makes more sense. Also please update the comments to reflect the effects of this setting on the metric name with a example, similar to the one in the `application` setting.