[errors] Greatly simplify common/errors package.

logdog/client/cmd/logdog_butler/output_logdog.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 main
 
 import (
         "fmt"
         "time"
 
@@ skipping 31 matching lines @@
         // TODO(dnj): Default to false when mandatory debugging is finished.
         flags.BoolVar(&f.track, "track", true,
                 "Track each sent message and dump at the end. This adds CPU/memory overhead.")
 
         return opt
 }
 
 func (f *logdogOutputFactory) configOutput(a *application) (output.Output, error) {
         auth, err := a.authenticator(a)
         if err != nil {
-                return nil, errors.Annotate(err).Reason("failed to instantiate authenticator").Err()
+                return nil, errors.Annotate(err, "failed to instantiate authenticator").Err()
         }
 
         host := a.coordinatorHost
         if host == "" {
                 return nil, errors.New("logdog output requires a Coordinator host (-coordinator-host)")
         }
         if f.service != "" {
                 host = fmt.Sprintf("%s-dot-%s", f.service, host)
         }
 
         cfg := out.Config{
                 Auth:             auth,
                 Host:             host,
                 Project:          a.project,
                 Prefix:           a.prefix,
                 PrefixExpiration: time.Duration(f.prefixExpiration),
                 SourceInfo: []string{
                         "LogDog Butler",
                 },
                 PublishContext: a.ncCtx,
                 RPCTimeout:     30 * time.Second,
                 Track:          f.track,
         }
         return cfg.Register(a)
 }
 
 func (f *logdogOutputFactory) scopes() []string { return out.Scopes() }