Send requests to all carbonlink hosts when metric starts with CARBON_METRIC_PREFIX.

In a multi-carbon environment, the carbon stats are written by the carbon process that generates them and the consistent hash ring is ignored.  So, to gather the real-time stats we must ask all Carbon hosts for each carbon stat.
Merge pull request #417 from cbowman0/rfc/get-current-carbon-metrics

Rfc/get current carbon metrics