stats library very slow to reconnect when graphite endpoint goes down

[Dieterbe]

for Mt's internal stats, if the carbon endpoint goes down and back up, it seems to take 15-20 minutes for MT to notice. so there's a long gap of no stats which finally will get filled in, but it takes too long

[woodsaj]

I think this can be easily solved by calling conn.SetWriteDeadline(time.Now().Add(time.Second * 10)) before calling conn.Write() https://github.com/grafana/metrictank/blob/master/stats/out_graphite.go#L109