updeate metricPersist nsq handler to use multiple goroutines.
updeate metricPersist nsq handler to use multiple goroutines.

OOM-Killer/metrictank,raintank/raintank-metric,replay/metrictank,replay/metrictank,raintank/raintank-metric,OOM-Killer/metrictank,replay/metrictank,raintank/metrictank,raintank/metrictank,raintank/metrictank,OOM-Killer/metrictank,raintank/metrictank,raintank/raintank-metric,replay/metrictank