[errors] Greatly simplify common/errors package.

deploytool/cmd/luci_deploy/tools.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 main
 
 import (
         "os"
         "os/exec"
         "path/filepath"
@@ skipping 30 matching lines @@
                 }
 
                 if t.pathMap == nil {
                         t.pathMap = make(map[string]string)
                 }
                 t.pathMap[command] = path
         }
 
         if path == "" {
                 // Lookup was attempted, but tool could not be found.
-                return "", errors.Reason("tool %(toolName)q is not available").D("toolName", command).Err()
+                return "", errors.Reason("tool %q is not available", command).Err()
         }
         return path, nil
 }
 
 func (t *tools) genericTool(name string) (*genericTool, error) {
         exe, err := t.getLookup(name)
         if err != nil {
                 return nil, err
         }
         return &genericTool{
@@ skipping 104 matching lines @@
 
 func (t *gitTool) getRevListCount(c context.Context, gitDir string) (int, error) {
         x := t.exec(gitDir, "rev-list", "--count", "HEAD")
         if err := x.check(c); err != nil {
                 return 0, err
         }
 
         output := strings.TrimSpace(x.stdout.String())
         v, err := strconv.Atoi(output)
         if err != nil {
-                return 0, errors.Annotate(err).Reason("failed to parse rev-list count").D("output", output).Err()
+                return 0, errors.Annotate(err, "failed to parse rev-list count").
+                        InternalReason("output(%s)", output).Err()
         }
         return v, nil
 }
 
 type goTool struct {
         exe    string
         goPath []string
 }
 
 func (t *goTool) exec(subCommand string, args ...string) *workExecutor {
@@ skipping 23 matching lines @@
 }
 
 type gcloudTool struct {
         exe     string
         project string
 }
 
 func (t *gcloudTool) exec(command string, args ...string) *workExecutor {
         return execute(t.exe, append([]string{"--project", t.project, command}, args...)...)
 }