statsd-proxy: delete state of metrics on ring members change (add or remove)

Currently when statsd proxy ring status is changing (statsd instances was adding or removing from the ring) , the state for all other statsd instances remain as is. This could lead to unexpected behavior like sending same metrics twice by different backend.

Current solution is to set deleteIdleStats: true in StatsD configuration file. Deleting statsd state while ring member change will turn the behavior to be event driven over passive approach.