LogDog: Implement prefix registration in Butler.

client/cmd/logdog_butler/subcommand_serve.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 main
 
 import (
         "github.com/luci/luci-go/client/internal/logdog/butler"
         log "github.com/luci/luci-go/common/logging"
         "github.com/maruel/subcommands"
@@ skipping 28 matching lines @@
                 }.Errorf(a, "Invalid stream server URI.")
                 return configErrorReturnCode
         }
         streamServer := createStreamServer(a, cmd.uri)
 
         if err := streamServer.Listen(); err != nil {
                 log.Errorf(log.SetError(a, err), "Failed to connect to stream server.")
                 return runtimeErrorReturnCode
         }
 
-        a.Main(func(b *butler.Butler) error {
+        // We think everything will work. Configure our Output instance.
+        output, err := a.configOutput()
+        if err != nil {
+                log.WithError(err).Errorf(a, "Failed to create output instance.")
+                return runtimeErrorReturnCode
+        }
+        defer output.Close()
+
+        a.runWithButler(output, func(b *butler.Butler) error {
                 b.AddStreamServer(streamServer)
                 return nil
         })
 
         return 0
 }