Convert to new stats_hero supporting custom module config

The sf/modular-config branch of stats_hero removes hard-coding of
module names used for metric aggregation along with a few other minor
improvements.

This PR includes the changes required to use the new stats_hero.

A few of the commits will be updated prior to merge since we will
merge stats_hero to master and same for chef_wm.

I built a local deb using omnibus-chef, verified a full pedant
run, and drove some traffic at it to verify that metrics appear in
graphite.