[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/apply_auth.go b/vendor/go.etcd.io/etcd/etcdserver/apply_auth.go
new file mode 100644
index 0000000..4b094ad
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/etcdserver/apply_auth.go
@@ -0,0 +1,242 @@
+// Copyright 2016 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 etcdserver
+
+import (
+	"sync"
+
+	"go.etcd.io/etcd/auth"
+	pb "go.etcd.io/etcd/etcdserver/etcdserverpb"
+	"go.etcd.io/etcd/lease"
+	"go.etcd.io/etcd/mvcc"
+)
+
+type authApplierV3 struct {
+	applierV3
+	as     auth.AuthStore
+	lessor lease.Lessor
+
+	// mu serializes Apply so that user isn't corrupted and so that
+	// serialized requests don't leak data from TOCTOU errors
+	mu sync.Mutex
+
+	authInfo auth.AuthInfo
+}
+
+func newAuthApplierV3(as auth.AuthStore, base applierV3, lessor lease.Lessor) *authApplierV3 {
+	return &authApplierV3{applierV3: base, as: as, lessor: lessor}
+}
+
+func (aa *authApplierV3) Apply(r *pb.InternalRaftRequest) *applyResult {
+	aa.mu.Lock()
+	defer aa.mu.Unlock()
+	if r.Header != nil {
+		// backward-compatible with pre-3.0 releases when internalRaftRequest
+		// does not have header field
+		aa.authInfo.Username = r.Header.Username
+		aa.authInfo.Revision = r.Header.AuthRevision
+	}
+	if needAdminPermission(r) {
+		if err := aa.as.IsAdminPermitted(&aa.authInfo); err != nil {
+			aa.authInfo.Username = ""
+			aa.authInfo.Revision = 0
+			return &applyResult{err: err}
+		}
+	}
+	ret := aa.applierV3.Apply(r)
+	aa.authInfo.Username = ""
+	aa.authInfo.Revision = 0
+	return ret
+}
+
+func (aa *authApplierV3) Put(txn mvcc.TxnWrite, r *pb.PutRequest) (*pb.PutResponse, error) {
+	if err := aa.as.IsPutPermitted(&aa.authInfo, r.Key); err != nil {
+		return nil, err
+	}
+
+	if err := aa.checkLeasePuts(lease.LeaseID(r.Lease)); err != nil {
+		// The specified lease is already attached with a key that cannot
+		// be written by this user. It means the user cannot revoke the
+		// lease so attaching the lease to the newly written key should
+		// be forbidden.
+		return nil, err
+	}
+
+	if r.PrevKv {
+		err := aa.as.IsRangePermitted(&aa.authInfo, r.Key, nil)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return aa.applierV3.Put(txn, r)
+}
+
+func (aa *authApplierV3) Range(txn mvcc.TxnRead, r *pb.RangeRequest) (*pb.RangeResponse, error) {
+	if err := aa.as.IsRangePermitted(&aa.authInfo, r.Key, r.RangeEnd); err != nil {
+		return nil, err
+	}
+	return aa.applierV3.Range(txn, r)
+}
+
+func (aa *authApplierV3) DeleteRange(txn mvcc.TxnWrite, r *pb.DeleteRangeRequest) (*pb.DeleteRangeResponse, error) {
+	if err := aa.as.IsDeleteRangePermitted(&aa.authInfo, r.Key, r.RangeEnd); err != nil {
+		return nil, err
+	}
+	if r.PrevKv {
+		err := aa.as.IsRangePermitted(&aa.authInfo, r.Key, r.RangeEnd)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return aa.applierV3.DeleteRange(txn, r)
+}
+
+func checkTxnReqsPermission(as auth.AuthStore, ai *auth.AuthInfo, reqs []*pb.RequestOp) error {
+	for _, requ := range reqs {
+		switch tv := requ.Request.(type) {
+		case *pb.RequestOp_RequestRange:
+			if tv.RequestRange == nil {
+				continue
+			}
+
+			if err := as.IsRangePermitted(ai, tv.RequestRange.Key, tv.RequestRange.RangeEnd); err != nil {
+				return err
+			}
+
+		case *pb.RequestOp_RequestPut:
+			if tv.RequestPut == nil {
+				continue
+			}
+
+			if err := as.IsPutPermitted(ai, tv.RequestPut.Key); err != nil {
+				return err
+			}
+
+		case *pb.RequestOp_RequestDeleteRange:
+			if tv.RequestDeleteRange == nil {
+				continue
+			}
+
+			if tv.RequestDeleteRange.PrevKv {
+				err := as.IsRangePermitted(ai, tv.RequestDeleteRange.Key, tv.RequestDeleteRange.RangeEnd)
+				if err != nil {
+					return err
+				}
+			}
+
+			err := as.IsDeleteRangePermitted(ai, tv.RequestDeleteRange.Key, tv.RequestDeleteRange.RangeEnd)
+			if err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+func checkTxnAuth(as auth.AuthStore, ai *auth.AuthInfo, rt *pb.TxnRequest) error {
+	for _, c := range rt.Compare {
+		if err := as.IsRangePermitted(ai, c.Key, c.RangeEnd); err != nil {
+			return err
+		}
+	}
+	if err := checkTxnReqsPermission(as, ai, rt.Success); err != nil {
+		return err
+	}
+	return checkTxnReqsPermission(as, ai, rt.Failure)
+}
+
+func (aa *authApplierV3) Txn(rt *pb.TxnRequest) (*pb.TxnResponse, error) {
+	if err := checkTxnAuth(aa.as, &aa.authInfo, rt); err != nil {
+		return nil, err
+	}
+	return aa.applierV3.Txn(rt)
+}
+
+func (aa *authApplierV3) LeaseRevoke(lc *pb.LeaseRevokeRequest) (*pb.LeaseRevokeResponse, error) {
+	if err := aa.checkLeasePuts(lease.LeaseID(lc.ID)); err != nil {
+		return nil, err
+	}
+	return aa.applierV3.LeaseRevoke(lc)
+}
+
+func (aa *authApplierV3) checkLeasePuts(leaseID lease.LeaseID) error {
+	lease := aa.lessor.Lookup(leaseID)
+	if lease != nil {
+		for _, key := range lease.Keys() {
+			if err := aa.as.IsPutPermitted(&aa.authInfo, []byte(key)); err != nil {
+				return err
+			}
+		}
+	}
+
+	return nil
+}
+
+func (aa *authApplierV3) UserGet(r *pb.AuthUserGetRequest) (*pb.AuthUserGetResponse, error) {
+	err := aa.as.IsAdminPermitted(&aa.authInfo)
+	if err != nil && r.Name != aa.authInfo.Username {
+		aa.authInfo.Username = ""
+		aa.authInfo.Revision = 0
+		return &pb.AuthUserGetResponse{}, err
+	}
+
+	return aa.applierV3.UserGet(r)
+}
+
+func (aa *authApplierV3) RoleGet(r *pb.AuthRoleGetRequest) (*pb.AuthRoleGetResponse, error) {
+	err := aa.as.IsAdminPermitted(&aa.authInfo)
+	if err != nil && !aa.as.HasRole(aa.authInfo.Username, r.Role) {
+		aa.authInfo.Username = ""
+		aa.authInfo.Revision = 0
+		return &pb.AuthRoleGetResponse{}, err
+	}
+
+	return aa.applierV3.RoleGet(r)
+}
+
+func needAdminPermission(r *pb.InternalRaftRequest) bool {
+	switch {
+	case r.AuthEnable != nil:
+		return true
+	case r.AuthDisable != nil:
+		return true
+	case r.AuthUserAdd != nil:
+		return true
+	case r.AuthUserDelete != nil:
+		return true
+	case r.AuthUserChangePassword != nil:
+		return true
+	case r.AuthUserGrantRole != nil:
+		return true
+	case r.AuthUserRevokeRole != nil:
+		return true
+	case r.AuthRoleAdd != nil:
+		return true
+	case r.AuthRoleGrantPermission != nil:
+		return true
+	case r.AuthRoleRevokePermission != nil:
+		return true
+	case r.AuthRoleDelete != nil:
+		return true
+	case r.AuthUserList != nil:
+		return true
+	case r.AuthRoleList != nil:
+		return true
+	default:
+		return false
+	}
+}