[errors] Greatly simplify common/errors package.

logdog/client/cli/main.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 cli
 
 import (
         "flag"
         "fmt"
         "net/http"
@@ skipping 105 matching lines @@
         default:
                 return "", errors.New("a Coordinator host must be specified (-host)")
         }
 }
 
 // coordinatorClient returns a Coordinator client for the specified host. If
 // no host is provided, the command-line host will be used.
 func (a *application) coordinatorClient(host string) (*coordinator.Client, error) {
         host, err := a.resolveHost(host)
         if err != nil {
-                return nil, errors.Annotate(err).Err()
+                return nil, errors.Annotate(err, "").Err()
         }
 
         // Get our Coordinator client instance.
         prpcClient := prpc.Client{
                 C:       a.httpClient,
                 Host:    host,
                 Options: prpc.DefaultOptions(),
         }
         prpcClient.Options.Insecure = a.insecure
         return coordinator.NewClient(&prpcClient), nil
@@ skipping 82 matching lines @@
         }
 
         if a.httpClient, err = auth.NewAuthenticator(ctx, auth.OptionalLogin, authOpts).Client(); err != nil {
                 log.Errorf(log.SetError(ctx, err), "Failed to create authenticated client.")
                 return 1
         }
 
         a.Context = ctx
         return subcommands.Run(&a, flags.Args())
 }