refactor: openpitrix module

Signed-off-by: hongming <talonwan@yunify.com>

vendor/openpitrix.io/openpitrix/pkg/util/stringutil/base64.go

@@ -0,0 +1,15 @@
+// Copyright 2018 The OpenPitrix Authors. All rights reserved.
+// Use of this source code is governed by a Apache license
+// that can be found in the LICENSE file.
+
+package stringutil
+
+import (
+	"bytes"
+	"encoding/base64"
+	"io/ioutil"
+)
+
+func DecodeBase64(i string) ([]byte, error) {
+	return ioutil.ReadAll(base64.NewDecoder(base64.StdEncoding, bytes.NewBufferString(i)))
+}