[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/go.etcd.io/etcd/mvcc/metrics_txn.go b/vendor/go.etcd.io/etcd/mvcc/metrics_txn.go
new file mode 100644
index 0000000..64b629c
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/mvcc/metrics_txn.go
@@ -0,0 +1,67 @@
+// Copyright 2017 The etcd Authors
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package mvcc
+
+import "go.etcd.io/etcd/lease"
+
+type metricsTxnWrite struct {
+	TxnWrite
+	ranges  uint
+	puts    uint
+	deletes uint
+}
+
+func newMetricsTxnRead(tr TxnRead) TxnRead {
+	return &metricsTxnWrite{&txnReadWrite{tr}, 0, 0, 0}
+}
+
+func newMetricsTxnWrite(tw TxnWrite) TxnWrite {
+	return &metricsTxnWrite{tw, 0, 0, 0}
+}
+
+func (tw *metricsTxnWrite) Range(key, end []byte, ro RangeOptions) (*RangeResult, error) {
+	tw.ranges++
+	return tw.TxnWrite.Range(key, end, ro)
+}
+
+func (tw *metricsTxnWrite) DeleteRange(key, end []byte) (n, rev int64) {
+	tw.deletes++
+	return tw.TxnWrite.DeleteRange(key, end)
+}
+
+func (tw *metricsTxnWrite) Put(key, value []byte, lease lease.LeaseID) (rev int64) {
+	tw.puts++
+	return tw.TxnWrite.Put(key, value, lease)
+}
+
+func (tw *metricsTxnWrite) End() {
+	defer tw.TxnWrite.End()
+	if sum := tw.ranges + tw.puts + tw.deletes; sum > 1 {
+		txnCounter.Inc()
+		txnCounterDebug.Inc() // TODO: remove in 3.5 release
+	}
+
+	ranges := float64(tw.ranges)
+	rangeCounter.Add(ranges)
+	rangeCounterDebug.Add(ranges) // TODO: remove in 3.5 release
+
+	puts := float64(tw.puts)
+	putCounter.Add(puts)
+	putCounterDebug.Add(puts) // TODO: remove in 3.5 release
+
+	deletes := float64(tw.deletes)
+	deleteCounter.Add(deletes)
+	deleteCounterDebug.Add(deletes) // TODO: remove in 3.5 release
+}