Memory leak when broker authenticate failed

[Stephan14]

		b.incomingByteRate = metrics.GetOrRegisterMeter("incoming-byte-rate", conf.MetricRegistry)
		b.requestRate = metrics.GetOrRegisterMeter("request-rate", conf.MetricRegistry)
		b.requestSize = getOrRegisterHistogram("request-size", conf.MetricRegistry)
		b.requestLatency = getOrRegisterHistogram("request-latency-in-ms", conf.MetricRegistry)
		b.outgoingByteRate = metrics.GetOrRegisterMeter("outgoing-byte-rate", conf.MetricRegistry)
		b.responseRate = metrics.GetOrRegisterMeter("response-rate", conf.MetricRegistry)
		b.responseSize = getOrRegisterHistogram("response-size", conf.MetricRegistry)
		b.requestsInFlight = metrics.GetOrRegisterCounter("requests-in-flight", conf.MetricRegistry)
		// Do not gather metrics for seeded broker (only used during bootstrap) because they share
		// the same id (-1) and are already exposed through the global metrics above
		if b.id >= 0 {
			b.registerMetrics()
		}

		if conf.Net.SASL.Enable {
			b.connErr = b.authenticateViaSASL()

			if b.connErr != nil {
				err = b.conn.Close()
				if err == nil {
					Logger.Printf("Closed connection to broker %s\n", b.addr)
				} else {
					Logger.Printf("Error while closing connection to broker %s: %s\n", b.addr, err)
				}
				b.conn = nil
				atomic.StoreInt32(&b.opened, 0)
				return
			}
		}

Broker register metrics name to registeredMetrics and then authenticate to broker by socket, when authenticate failed many times, the registeredMetrics is slice and will append a metrics name many times