[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/github.com/modern-go/reflect2/safe_field.go b/vendor/github.com/modern-go/reflect2/safe_field.go
new file mode 100644
index 0000000..d4ba1f4
--- /dev/null
+++ b/vendor/github.com/modern-go/reflect2/safe_field.go
@@ -0,0 +1,58 @@
+package reflect2
+
+import (
+	"reflect"
+	"unsafe"
+)
+
+type safeField struct {
+	reflect.StructField
+}
+
+func (field *safeField) Offset() uintptr {
+	return field.StructField.Offset
+}
+
+func (field *safeField) Name() string {
+	return field.StructField.Name
+}
+
+func (field *safeField) PkgPath() string {
+	return field.StructField.PkgPath
+}
+
+func (field *safeField) Type() Type {
+	panic("not implemented")
+}
+
+func (field *safeField) Tag() reflect.StructTag {
+	return field.StructField.Tag
+}
+
+func (field *safeField) Index() []int {
+	return field.StructField.Index
+}
+
+func (field *safeField) Anonymous() bool {
+	return field.StructField.Anonymous
+}
+
+func (field *safeField) Set(obj interface{}, value interface{}) {
+	val := reflect.ValueOf(obj).Elem()
+	val.FieldByIndex(field.Index()).Set(reflect.ValueOf(value).Elem())
+}
+
+func (field *safeField) UnsafeSet(obj unsafe.Pointer, value unsafe.Pointer) {
+	panic("unsafe operation is not supported")
+}
+
+func (field *safeField) Get(obj interface{}) interface{} {
+	val := reflect.ValueOf(obj).Elem().FieldByIndex(field.Index())
+	ptr := reflect.New(val.Type())
+	ptr.Elem().Set(val)
+	return ptr.Interface()
+}
+
+func (field *safeField) UnsafeGet(obj unsafe.Pointer) unsafe.Pointer {
+	panic("does not support unsafe operation")
+}