Move multierror logic into luci-go.

common/parallel/parallel_test.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 parallel
 
 import (
         "fmt"
 )
 
 func ExampleFanOutIn() {
         data := []int{1, 20}
         err := FanOutIn(func(ch chan<- func() error) {
                 for _, d := range data {
                         d := d
                         ch <- func() error {
                                 if d > 10 {
                                         return fmt.Errorf("%d is over 10", d)
                                 }
                                 return nil
                         }
                 }
         })
 
-        fmt.Printf("got: %s", err)
-        // Output: got: ["20 is over 10"]
+        fmt.Printf("got: %q", err)
+        // Output: got: "20 is over 10"
 }