Update APIs to use new Google cloud paths.

common/auth/auth.go

 // Copyright 2015 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 // Package auth implements an opinionated wrapper around OAuth2.
 //
 // It hides configurability of base oauth2 library and instead makes a
 // predefined set of choices regarding where the credentials should be stored,
 // how they should be cached and how OAuth2 flow should be invoked.
 //
@@ skipping 20 matching lines @@
         "net/http"
         "os"
         "path/filepath"
         "sort"
         "sync"
         "time"
 
         "golang.org/x/net/context"
         "golang.org/x/oauth2"
 
-        "google.golang.org/cloud/compute/metadata"
+        "cloud.google.com/go/compute/metadata"
 
         "github.com/mitchellh/go-homedir"
 
         "github.com/luci/luci-go/common/auth/internal"
         "github.com/luci/luci-go/common/clock"
         "github.com/luci/luci-go/common/logging"
         "github.com/luci/luci-go/common/retry"
 )
 
 var (
@@ skipping 780 matching lines @@
 }
 
 // SecretsDir returns an absolute path to a directory to keep secret files in.
 func SecretsDir() string {
         home, err := homedir.Dir()
         if err != nil {
                 panic(err.Error())
         }
         return filepath.Join(home, ".config", "chrome_infra", "auth")
 }