Back-feed gauge stats back into statsite

Statsite does not treat gauges the same way that statsd does. When
statsite flushes stats to the sinks, it clears the gauges back to 0.
Armon recommended in [0] to have the sink send gauges back into statsite
to seed the value back to the previous value.

[0] https://github.com/armon/statsite/issues/69