[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/pkg/pbutil/pbutil.go b/vendor/go.etcd.io/etcd/pkg/pbutil/pbutil.go
new file mode 100644
index 0000000..53167ff
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/pkg/pbutil/pbutil.go
@@ -0,0 +1,60 @@
+// 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 pbutil defines interfaces for handling Protocol Buffer objects.
+package pbutil
+
+import "github.com/coreos/pkg/capnslog"
+
+var (
+	plog = capnslog.NewPackageLogger("go.etcd.io/etcd", "pkg/pbutil")
+)
+
+type Marshaler interface {
+	Marshal() (data []byte, err error)
+}
+
+type Unmarshaler interface {
+	Unmarshal(data []byte) error
+}
+
+func MustMarshal(m Marshaler) []byte {
+	d, err := m.Marshal()
+	if err != nil {
+		plog.Panicf("marshal should never fail (%v)", err)
+	}
+	return d
+}
+
+func MustUnmarshal(um Unmarshaler, data []byte) {
+	if err := um.Unmarshal(data); err != nil {
+		plog.Panicf("unmarshal should never fail (%v)", err)
+	}
+}
+
+func MaybeUnmarshal(um Unmarshaler, data []byte) bool {
+	if err := um.Unmarshal(data); err != nil {
+		return false
+	}
+	return true
+}
+
+func GetBool(v *bool) (vv bool, set bool) {
+	if v == nil {
+		return false, false
+	}
+	return *v, true
+}
+
+func Boolp(b bool) *bool { return &b }