[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/kvstore_compaction.go b/vendor/go.etcd.io/etcd/mvcc/kvstore_compaction.go
new file mode 100644
index 0000000..2adb498
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/mvcc/kvstore_compaction.go
@@ -0,0 +1,79 @@
+// Copyright 2015 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 (
+	"encoding/binary"
+	"time"
+
+	"go.uber.org/zap"
+)
+
+func (s *store) scheduleCompaction(compactMainRev int64, keep map[revision]struct{}) bool {
+	totalStart := time.Now()
+	defer func() { dbCompactionTotalMs.Observe(float64(time.Since(totalStart) / time.Millisecond)) }()
+	keyCompactions := 0
+	defer func() { dbCompactionKeysCounter.Add(float64(keyCompactions)) }()
+
+	end := make([]byte, 8)
+	binary.BigEndian.PutUint64(end, uint64(compactMainRev+1))
+
+	last := make([]byte, 8+1+8)
+	for {
+		var rev revision
+
+		start := time.Now()
+
+		tx := s.b.BatchTx()
+		tx.Lock()
+		keys, _ := tx.UnsafeRange(keyBucketName, last, end, int64(s.cfg.CompactionBatchLimit))
+		for _, key := range keys {
+			rev = bytesToRev(key)
+			if _, ok := keep[rev]; !ok {
+				tx.UnsafeDelete(keyBucketName, key)
+			}
+		}
+
+		if len(keys) < s.cfg.CompactionBatchLimit {
+			rbytes := make([]byte, 8+1+8)
+			revToBytes(revision{main: compactMainRev}, rbytes)
+			tx.UnsafePut(metaBucketName, finishedCompactKeyName, rbytes)
+			tx.Unlock()
+			if s.lg != nil {
+				s.lg.Info(
+					"finished scheduled compaction",
+					zap.Int64("compact-revision", compactMainRev),
+					zap.Duration("took", time.Since(totalStart)),
+				)
+			} else {
+				plog.Infof("finished scheduled compaction at %d (took %v)", compactMainRev, time.Since(totalStart))
+			}
+			return true
+		}
+
+		// update last
+		revToBytes(revision{main: rev.main, sub: rev.sub + 1}, last)
+		tx.Unlock()
+		// Immediately commit the compaction deletes instead of letting them accumulate in the write buffer
+		s.b.ForceCommit()
+		dbCompactionPauseMs.Observe(float64(time.Since(start) / time.Millisecond))
+
+		select {
+		case <-time.After(10 * time.Millisecond):
+		case <-s.stopc:
+			return false
+		}
+	}
+}