[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/membership/member.go b/vendor/go.etcd.io/etcd/etcdserver/api/membership/member.go
new file mode 100644
index 0000000..896cb36
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/etcdserver/api/membership/member.go
@@ -0,0 +1,142 @@
+// 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 membership
+
+import (
+	"crypto/sha1"
+	"encoding/binary"
+	"fmt"
+	"math/rand"
+	"sort"
+	"time"
+
+	"github.com/coreos/pkg/capnslog"
+	"go.etcd.io/etcd/pkg/types"
+)
+
+var (
+	plog = capnslog.NewPackageLogger("go.etcd.io/etcd/v3", "etcdserver/membership")
+)
+
+// RaftAttributes represents the raft related attributes of an etcd member.
+type RaftAttributes struct {
+	// PeerURLs is the list of peers in the raft cluster.
+	// TODO(philips): ensure these are URLs
+	PeerURLs []string `json:"peerURLs"`
+	// IsLearner indicates if the member is raft learner.
+	IsLearner bool `json:"isLearner,omitempty"`
+}
+
+// Attributes represents all the non-raft related attributes of an etcd member.
+type Attributes struct {
+	Name       string   `json:"name,omitempty"`
+	ClientURLs []string `json:"clientURLs,omitempty"`
+}
+
+type Member struct {
+	ID types.ID `json:"id"`
+	RaftAttributes
+	Attributes
+}
+
+// NewMember creates a Member without an ID and generates one based on the
+// cluster name, peer URLs, and time. This is used for bootstrapping/adding new member.
+func NewMember(name string, peerURLs types.URLs, clusterName string, now *time.Time) *Member {
+	return newMember(name, peerURLs, clusterName, now, false)
+}
+
+// NewMemberAsLearner creates a learner Member without an ID and generates one based on the
+// cluster name, peer URLs, and time. This is used for adding new learner member.
+func NewMemberAsLearner(name string, peerURLs types.URLs, clusterName string, now *time.Time) *Member {
+	return newMember(name, peerURLs, clusterName, now, true)
+}
+
+func newMember(name string, peerURLs types.URLs, clusterName string, now *time.Time, isLearner bool) *Member {
+	m := &Member{
+		RaftAttributes: RaftAttributes{
+			PeerURLs:  peerURLs.StringSlice(),
+			IsLearner: isLearner,
+		},
+		Attributes: Attributes{Name: name},
+	}
+
+	var b []byte
+	sort.Strings(m.PeerURLs)
+	for _, p := range m.PeerURLs {
+		b = append(b, []byte(p)...)
+	}
+
+	b = append(b, []byte(clusterName)...)
+	if now != nil {
+		b = append(b, []byte(fmt.Sprintf("%d", now.Unix()))...)
+	}
+
+	hash := sha1.Sum(b)
+	m.ID = types.ID(binary.BigEndian.Uint64(hash[:8]))
+	return m
+}
+
+// PickPeerURL chooses a random address from a given Member's PeerURLs.
+// It will panic if there is no PeerURLs available in Member.
+func (m *Member) PickPeerURL() string {
+	if len(m.PeerURLs) == 0 {
+		panic("member should always have some peer url")
+	}
+	return m.PeerURLs[rand.Intn(len(m.PeerURLs))]
+}
+
+func (m *Member) Clone() *Member {
+	if m == nil {
+		return nil
+	}
+	mm := &Member{
+		ID: m.ID,
+		RaftAttributes: RaftAttributes{
+			IsLearner: m.IsLearner,
+		},
+		Attributes: Attributes{
+			Name: m.Name,
+		},
+	}
+	if m.PeerURLs != nil {
+		mm.PeerURLs = make([]string, len(m.PeerURLs))
+		copy(mm.PeerURLs, m.PeerURLs)
+	}
+	if m.ClientURLs != nil {
+		mm.ClientURLs = make([]string, len(m.ClientURLs))
+		copy(mm.ClientURLs, m.ClientURLs)
+	}
+	return mm
+}
+
+func (m *Member) IsStarted() bool {
+	return len(m.Name) != 0
+}
+
+// MembersByID implements sort by ID interface
+type MembersByID []*Member
+
+func (ms MembersByID) Len() int           { return len(ms) }
+func (ms MembersByID) Less(i, j int) bool { return ms[i].ID < ms[j].ID }
+func (ms MembersByID) Swap(i, j int)      { ms[i], ms[j] = ms[j], ms[i] }
+
+// MembersByPeerURLs implements sort by peer urls interface
+type MembersByPeerURLs []*Member
+
+func (ms MembersByPeerURLs) Len() int { return len(ms) }
+func (ms MembersByPeerURLs) Less(i, j int) bool {
+	return ms[i].PeerURLs[0] < ms[j].PeerURLs[0]
+}
+func (ms MembersByPeerURLs) Swap(i, j int) { ms[i], ms[j] = ms[j], ms[i] }