Move retry and lhttp packages from client/internal to common/.

client/internal/lhttp/utils.go

-// Copyright 2015 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-package lhttp
-
-import (
-        "errors"
-        "net/url"
-        "strings"
-)
-
-// URLToHTTPS ensures the url is https://.
-func URLToHTTPS(s string) (string, error) {
-        u, err := url.Parse(s)
-        if err != nil {
-                return "", err
-        }
-        if u.Scheme != "" && u.Scheme != "https" {
-                return "", errors.New("Only https:// scheme is accepted. It can be omitted.")
-        }
-        if !strings.HasPrefix(s, "https://") {
-                s = "https://" + s
-        }
-        if _, err = url.Parse(s); err != nil {
-                return "", err
-        }
-        return s, nil
-}