[errors] de-specialize Transient in favor of Tags.

tokenserver/appengine/impl/machinetoken/rpc_mint_machine_token.go

 // Copyright 2016 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 machinetoken
 
 import (
         "crypto/x509"
         "fmt"
         "strings"
         "time"
 
         "github.com/golang/protobuf/proto"
         "golang.org/x/net/context"
         "google.golang.org/grpc"
         "google.golang.org/grpc/codes"
 
         "github.com/luci/gae/service/info"
         "github.com/luci/luci-go/common/clock"
-        "github.com/luci/luci-go/common/errors"
         "github.com/luci/luci-go/common/logging"
         "github.com/luci/luci-go/common/proto/google"
+        "github.com/luci/luci-go/common/retry"
         "github.com/luci/luci-go/server/auth"
         "github.com/luci/luci-go/server/auth/signing"
 
         tokenserver "github.com/luci/luci-go/tokenserver/api"
         "github.com/luci/luci-go/tokenserver/api/admin/v1"
         "github.com/luci/luci-go/tokenserver/api/minter/v1"
 
         "github.com/luci/luci-go/tokenserver/appengine/impl/certchecker"
         "github.com/luci/luci-go/tokenserver/appengine/impl/certconfig"
         "github.com/luci/luci-go/tokenserver/appengine/impl/utils"
@@ skipping 176 matching lines @@
                         TokenResponse: &minter.MachineTokenResponse{
                                 ServiceVersion: serviceVer,
                                 TokenType: &minter.MachineTokenResponse_LuciMachineToken{
                                         LuciMachineToken: &minter.LuciMachineToken{
                                                 MachineToken: signedToken,
                                                 Expiry:       google.NewTimestamp(expiry),
                                         },
                                 },
                         },
                 }, body, nil
-        case errors.IsTransient(err):
+        case retry.Tag.In(err):
                 return nil, nil, grpc.Errorf(codes.Internal, "failed to generate machine token - %s", err)
         default:
                 resp, err := r.mintingErrorResponse(c, minter.ErrorCode_MACHINE_TOKEN_MINTING_ERROR, "%s", err)
                 return resp, nil, err
         }
 }
 
 func (r *MintMachineTokenRPC) mintingErrorResponse(c context.Context, code minter.ErrorCode, msg string, args ...interface{}) (*minter.MintMachineTokenResponse, error) {
         serviceVer, err := utils.ServiceVersion(c, r.Signer)
         if err != nil {
                 return nil, grpc.Errorf(codes.Internal, "can't grab service version - %s", err)
         }
         return &minter.MintMachineTokenResponse{
                 ErrorCode:      code,
                 ErrorMessage:   fmt.Sprintf(msg, args...),
                 ServiceVersion: serviceVer,
         }, nil
 }