Move multierror logic into luci-go.

common/errors/errors_test.go

Index: common/errors/errors_test.go
diff --git a/common/errors/errors_test.go b/common/errors/errors_test.go
index e8657fd882dee348eedd2f497f733e32f39190fa..b3e8890fb614b73ea88f7226ffdff7f8b4cd9c1f 100644
--- a/common/errors/errors_test.go
+++ b/common/errors/errors_test.go
@@ -35,17 +35,17 @@ func TestMultiError(t *testing.T) {
 	Convey("MultiError works", t, func() {
 		var me error = MultiError{fmt.Errorf("hello"), fmt.Errorf("bob")}
 
-		So(me.Error(), ShouldEqual, `["hello" "bob"]`)
+		So(me.Error(), ShouldEqual, `hello (and 1 other error)`)
 
 		Convey("MultiErrorFromErrors with errors works", func() {
 			mec := make(chan error, 5)
-			mec <- fmt.Errorf("what")
-			mec <- nil
 			mec <- MakeMarkFn("multiErr")("one-off")
+			mec <- nil
+			mec <- fmt.Errorf("what")
 			close(mec)
 
 			err := MultiErrorFromErrors(mec)
-			So(err.Error(), ShouldEqual, `["what" "multiErr - errors_test.go:44 - one-off"]`)
+			So(err.Error(), ShouldEqual, `multiErr - errors_test.go:42 - one-off (and 1 other error)`)
 		})
 
 		Convey("MultiErrorFromErrors with nil works", func() {
@@ -97,6 +97,6 @@ func ExampleMultiError() {
 	fmt.Printf("got: %v\n", err)
 
 	// Output:
-	// got: ["what"] len=1
+	// got: what len=1
 	// got: <nil>
 }