[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/etcdhttp/base.go b/vendor/go.etcd.io/etcd/etcdserver/api/etcdhttp/base.go
new file mode 100644
index 0000000..c9df62e
--- /dev/null
+++ b/vendor/go.etcd.io/etcd/etcdserver/api/etcdhttp/base.go
@@ -0,0 +1,203 @@
+// 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 etcdhttp
+
+import (
+	"encoding/json"
+	"expvar"
+	"fmt"
+	"net/http"
+	"strings"
+
+	"go.etcd.io/etcd/etcdserver"
+	"go.etcd.io/etcd/etcdserver/api"
+	"go.etcd.io/etcd/etcdserver/api/v2error"
+	"go.etcd.io/etcd/etcdserver/api/v2http/httptypes"
+	"go.etcd.io/etcd/pkg/logutil"
+	"go.etcd.io/etcd/version"
+
+	"github.com/coreos/pkg/capnslog"
+	"go.uber.org/zap"
+)
+
+var (
+	plog = capnslog.NewPackageLogger("go.etcd.io/etcd", "etcdserver/api/etcdhttp")
+	mlog = logutil.NewMergeLogger(plog)
+)
+
+const (
+	configPath  = "/config"
+	varsPath    = "/debug/vars"
+	versionPath = "/version"
+)
+
+// HandleBasic adds handlers to a mux for serving JSON etcd client requests
+// that do not access the v2 store.
+func HandleBasic(mux *http.ServeMux, server etcdserver.ServerPeer) {
+	mux.HandleFunc(varsPath, serveVars)
+
+	// TODO: deprecate '/config/local/log' in v3.5
+	mux.HandleFunc(configPath+"/local/log", logHandleFunc)
+
+	HandleMetricsHealth(mux, server)
+	mux.HandleFunc(versionPath, versionHandler(server.Cluster(), serveVersion))
+}
+
+func versionHandler(c api.Cluster, fn func(http.ResponseWriter, *http.Request, string)) http.HandlerFunc {
+	return func(w http.ResponseWriter, r *http.Request) {
+		v := c.Version()
+		if v != nil {
+			fn(w, r, v.String())
+		} else {
+			fn(w, r, "not_decided")
+		}
+	}
+}
+
+func serveVersion(w http.ResponseWriter, r *http.Request, clusterV string) {
+	if !allowMethod(w, r, "GET") {
+		return
+	}
+	vs := version.Versions{
+		Server:  version.Version,
+		Cluster: clusterV,
+	}
+
+	w.Header().Set("Content-Type", "application/json")
+	b, err := json.Marshal(&vs)
+	if err != nil {
+		plog.Panicf("cannot marshal versions to json (%v)", err)
+	}
+	w.Write(b)
+}
+
+// TODO: deprecate '/config/local/log' in v3.5
+func logHandleFunc(w http.ResponseWriter, r *http.Request) {
+	if !allowMethod(w, r, "PUT") {
+		return
+	}
+
+	in := struct{ Level string }{}
+
+	d := json.NewDecoder(r.Body)
+	if err := d.Decode(&in); err != nil {
+		WriteError(nil, w, r, httptypes.NewHTTPError(http.StatusBadRequest, "Invalid json body"))
+		return
+	}
+
+	logl, err := capnslog.ParseLevel(strings.ToUpper(in.Level))
+	if err != nil {
+		WriteError(nil, w, r, httptypes.NewHTTPError(http.StatusBadRequest, "Invalid log level "+in.Level))
+		return
+	}
+
+	plog.Noticef("globalLogLevel set to %q", logl.String())
+	capnslog.SetGlobalLogLevel(logl)
+	w.WriteHeader(http.StatusNoContent)
+}
+
+func serveVars(w http.ResponseWriter, r *http.Request) {
+	if !allowMethod(w, r, "GET") {
+		return
+	}
+
+	w.Header().Set("Content-Type", "application/json; charset=utf-8")
+	fmt.Fprintf(w, "{\n")
+	first := true
+	expvar.Do(func(kv expvar.KeyValue) {
+		if !first {
+			fmt.Fprintf(w, ",\n")
+		}
+		first = false
+		fmt.Fprintf(w, "%q: %s", kv.Key, kv.Value)
+	})
+	fmt.Fprintf(w, "\n}\n")
+}
+
+func allowMethod(w http.ResponseWriter, r *http.Request, m string) bool {
+	if m == r.Method {
+		return true
+	}
+	w.Header().Set("Allow", m)
+	http.Error(w, "Method Not Allowed", http.StatusMethodNotAllowed)
+	return false
+}
+
+// WriteError logs and writes the given Error to the ResponseWriter
+// If Error is an etcdErr, it is rendered to the ResponseWriter
+// Otherwise, it is assumed to be a StatusInternalServerError
+func WriteError(lg *zap.Logger, w http.ResponseWriter, r *http.Request, err error) {
+	if err == nil {
+		return
+	}
+	switch e := err.(type) {
+	case *v2error.Error:
+		e.WriteTo(w)
+
+	case *httptypes.HTTPError:
+		if et := e.WriteTo(w); et != nil {
+			if lg != nil {
+				lg.Debug(
+					"failed to write v2 HTTP error",
+					zap.String("remote-addr", r.RemoteAddr),
+					zap.String("internal-server-error", e.Error()),
+					zap.Error(et),
+				)
+			} else {
+				plog.Debugf("error writing HTTPError (%v) to %s", et, r.RemoteAddr)
+			}
+		}
+
+	default:
+		switch err {
+		case etcdserver.ErrTimeoutDueToLeaderFail, etcdserver.ErrTimeoutDueToConnectionLost, etcdserver.ErrNotEnoughStartedMembers,
+			etcdserver.ErrUnhealthy:
+			if lg != nil {
+				lg.Warn(
+					"v2 response error",
+					zap.String("remote-addr", r.RemoteAddr),
+					zap.String("internal-server-error", err.Error()),
+				)
+			} else {
+				mlog.MergeError(err)
+			}
+
+		default:
+			if lg != nil {
+				lg.Warn(
+					"unexpected v2 response error",
+					zap.String("remote-addr", r.RemoteAddr),
+					zap.String("internal-server-error", err.Error()),
+				)
+			} else {
+				mlog.MergeErrorf("got unexpected response error (%v)", err)
+			}
+		}
+
+		herr := httptypes.NewHTTPError(http.StatusInternalServerError, "Internal Server Error")
+		if et := herr.WriteTo(w); et != nil {
+			if lg != nil {
+				lg.Debug(
+					"failed to write v2 HTTP error",
+					zap.String("remote-addr", r.RemoteAddr),
+					zap.String("internal-server-error", err.Error()),
+					zap.Error(et),
+				)
+			} else {
+				plog.Debugf("error writing HTTPError (%v) to %s", et, r.RemoteAddr)
+			}
+		}
+	}
+}