[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/v2v3/server.go b/vendor/go.etcd.io/etcd/etcdserver/api/v2v3/server.go
new file mode 100644
index 0000000..5ff9b96
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/etcdserver/api/v2v3/server.go
@@ -0,0 +1,129 @@
+// 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 v2v3
+
+import (
+	"context"
+	"net/http"
+	"time"
+
+	"go.etcd.io/etcd/clientv3"
+	"go.etcd.io/etcd/etcdserver"
+	"go.etcd.io/etcd/etcdserver/api"
+	"go.etcd.io/etcd/etcdserver/api/membership"
+	pb "go.etcd.io/etcd/etcdserver/etcdserverpb"
+	"go.etcd.io/etcd/pkg/types"
+
+	"github.com/coreos/go-semver/semver"
+	"go.uber.org/zap"
+)
+
+type fakeStats struct{}
+
+func (s *fakeStats) SelfStats() []byte   { return nil }
+func (s *fakeStats) LeaderStats() []byte { return nil }
+func (s *fakeStats) StoreStats() []byte  { return nil }
+
+type v2v3Server struct {
+	lg    *zap.Logger
+	c     *clientv3.Client
+	store *v2v3Store
+	fakeStats
+}
+
+func NewServer(lg *zap.Logger, c *clientv3.Client, pfx string) etcdserver.ServerPeer {
+	return &v2v3Server{lg: lg, c: c, store: newStore(c, pfx)}
+}
+
+func (s *v2v3Server) ClientCertAuthEnabled() bool { return false }
+
+func (s *v2v3Server) LeaseHandler() http.Handler { panic("STUB: lease handler") }
+func (s *v2v3Server) RaftHandler() http.Handler  { panic("STUB: raft handler") }
+
+func (s *v2v3Server) Leader() types.ID {
+	ctx, cancel := context.WithTimeout(context.TODO(), 5*time.Second)
+	defer cancel()
+	resp, err := s.c.Status(ctx, s.c.Endpoints()[0])
+	if err != nil {
+		return 0
+	}
+	return types.ID(resp.Leader)
+}
+
+func (s *v2v3Server) AddMember(ctx context.Context, memb membership.Member) ([]*membership.Member, error) {
+	// adding member as learner is not supported by V2 Server.
+	resp, err := s.c.MemberAdd(ctx, memb.PeerURLs)
+	if err != nil {
+		return nil, err
+	}
+	return v3MembersToMembership(resp.Members), nil
+}
+
+func (s *v2v3Server) RemoveMember(ctx context.Context, id uint64) ([]*membership.Member, error) {
+	resp, err := s.c.MemberRemove(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	return v3MembersToMembership(resp.Members), nil
+}
+
+func (s *v2v3Server) PromoteMember(ctx context.Context, id uint64) ([]*membership.Member, error) {
+	resp, err := s.c.MemberPromote(ctx, id)
+	if err != nil {
+		return nil, err
+	}
+	return v3MembersToMembership(resp.Members), nil
+}
+
+func (s *v2v3Server) UpdateMember(ctx context.Context, m membership.Member) ([]*membership.Member, error) {
+	resp, err := s.c.MemberUpdate(ctx, uint64(m.ID), m.PeerURLs)
+	if err != nil {
+		return nil, err
+	}
+	return v3MembersToMembership(resp.Members), nil
+}
+
+func v3MembersToMembership(v3membs []*pb.Member) []*membership.Member {
+	membs := make([]*membership.Member, len(v3membs))
+	for i, m := range v3membs {
+		membs[i] = &membership.Member{
+			ID: types.ID(m.ID),
+			RaftAttributes: membership.RaftAttributes{
+				PeerURLs:  m.PeerURLs,
+				IsLearner: m.IsLearner,
+			},
+			Attributes: membership.Attributes{
+				Name:       m.Name,
+				ClientURLs: m.ClientURLs,
+			},
+		}
+	}
+	return membs
+}
+
+func (s *v2v3Server) ClusterVersion() *semver.Version { return s.Version() }
+func (s *v2v3Server) Cluster() api.Cluster            { return s }
+func (s *v2v3Server) Alarms() []*pb.AlarmMember       { return nil }
+
+func (s *v2v3Server) Do(ctx context.Context, r pb.Request) (etcdserver.Response, error) {
+	applier := etcdserver.NewApplierV2(s.lg, s.store, nil)
+	reqHandler := etcdserver.NewStoreRequestV2Handler(s.store, applier)
+	req := (*etcdserver.RequestV2)(&r)
+	resp, err := req.Handle(ctx, reqHandler)
+	if resp.Err != nil {
+		return resp, resp.Err
+	}
+	return resp, err
+}