[VOL-2193] Create mocks for Kafka Client and Etcd

This commit consists of:
1) A kafka client mock that implements the kafka client interface
under voltha-lib-go/pkg/kafka/client.go
2) An embedded Etcd server that runs in-process and represents an
Etcd server.

Change-Id: I52a36132568e08c596bb4136918bebcb654a3b99
diff --git a/vendor/github.com/grpc-ecosystem/go-grpc-prometheus/client_reporter.go b/vendor/github.com/grpc-ecosystem/go-grpc-prometheus/client_reporter.go
new file mode 100644
index 0000000..cbf1532
--- /dev/null
+++ b/vendor/github.com/grpc-ecosystem/go-grpc-prometheus/client_reporter.go
@@ -0,0 +1,46 @@
+// Copyright 2016 Michal Witkowski. All Rights Reserved.
+// See LICENSE for licensing terms.
+
+package grpc_prometheus
+
+import (
+	"time"
+
+	"google.golang.org/grpc/codes"
+)
+
+type clientReporter struct {
+	metrics     *ClientMetrics
+	rpcType     grpcType
+	serviceName string
+	methodName  string
+	startTime   time.Time
+}
+
+func newClientReporter(m *ClientMetrics, rpcType grpcType, fullMethod string) *clientReporter {
+	r := &clientReporter{
+		metrics: m,
+		rpcType: rpcType,
+	}
+	if r.metrics.clientHandledHistogramEnabled {
+		r.startTime = time.Now()
+	}
+	r.serviceName, r.methodName = splitMethodName(fullMethod)
+	r.metrics.clientStartedCounter.WithLabelValues(string(r.rpcType), r.serviceName, r.methodName).Inc()
+	return r
+}
+
+func (r *clientReporter) ReceivedMessage() {
+	r.metrics.clientStreamMsgReceived.WithLabelValues(string(r.rpcType), r.serviceName, r.methodName).Inc()
+}
+
+func (r *clientReporter) SentMessage() {
+	r.metrics.clientStreamMsgSent.WithLabelValues(string(r.rpcType), r.serviceName, r.methodName).Inc()
+}
+
+func (r *clientReporter) Handled(code codes.Code) {
+	r.metrics.clientHandledCounter.WithLabelValues(string(r.rpcType), r.serviceName, r.methodName, code.String()).Inc()
+	if r.metrics.clientHandledHistogramEnabled {
+		r.metrics.clientHandledHistogram.WithLabelValues(string(r.rpcType), r.serviceName, r.methodName).Observe(time.Since(r.startTime).Seconds())
+	}
+}