[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/etcdserver/api/v3lock/lock.go b/vendor/go.etcd.io/etcd/etcdserver/api/v3lock/lock.go
new file mode 100644
index 0000000..5a17c86
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/etcdserver/api/v3lock/lock.go
@@ -0,0 +1,56 @@
+// 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 v3lock
+
+import (
+	"context"
+
+	"go.etcd.io/etcd/clientv3"
+	"go.etcd.io/etcd/clientv3/concurrency"
+	"go.etcd.io/etcd/etcdserver/api/v3lock/v3lockpb"
+)
+
+type lockServer struct {
+	c *clientv3.Client
+}
+
+func NewLockServer(c *clientv3.Client) v3lockpb.LockServer {
+	return &lockServer{c}
+}
+
+func (ls *lockServer) Lock(ctx context.Context, req *v3lockpb.LockRequest) (*v3lockpb.LockResponse, error) {
+	s, err := concurrency.NewSession(
+		ls.c,
+		concurrency.WithLease(clientv3.LeaseID(req.Lease)),
+		concurrency.WithContext(ctx),
+	)
+	if err != nil {
+		return nil, err
+	}
+	s.Orphan()
+	m := concurrency.NewMutex(s, string(req.Name))
+	if err = m.Lock(ctx); err != nil {
+		return nil, err
+	}
+	return &v3lockpb.LockResponse{Header: m.Header(), Key: []byte(m.Key())}, nil
+}
+
+func (ls *lockServer) Unlock(ctx context.Context, req *v3lockpb.UnlockRequest) (*v3lockpb.UnlockResponse, error) {
+	resp, err := ls.c.Delete(ctx, string(req.Key))
+	if err != nil {
+		return nil, err
+	}
+	return &v3lockpb.UnlockResponse{Header: resp.Header}, nil
+}