time: return ENOENT from androidLoadTzinfoFromTzdata if zone not found

This makes Android consistent with the change in CL 121877.

Updates #20969

Change-Id: I1f114556fd1d4654c8e4e6a59513bddd5dc3d1a0
Reviewed-on: https://go-review.googlesource.com/135416
Run-TryBot: Ian Lance Taylor <iant@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Elias Naur <elias.naur@gmail.com>

Author: ianlancetaylor

src/time/zoneinfo_android.go

@@ -11,6 +11,7 @@ package time
 import (
 	"errors"
 	"runtime"
+	"syscall"
 )
 
 var zoneSources = []string{
@@ -75,5 +76,5 @@ func androidLoadTzinfoFromTzdata(file, name string) ([]byte, error) {
 		}
 		return buf, nil
 	}
-	return nil, errors.New("cannot find " + name + " in tzdata file " + file)
+	return nil, syscall.ENOENT
 }