time: fix zone during windows test
Factor out sleep interrupt.

Fixes #1109.

R=alex.brainman, go.peter.90, mattn.jp
CC=golang-dev
https://golang.org/cl/4968041
diff --git a/src/pkg/time/sleep_test.go b/src/pkg/time/sleep_test.go
index a4a1a42..b6b88f6 100644
--- a/src/pkg/time/sleep_test.go
+++ b/src/pkg/time/sleep_test.go
@@ -7,7 +7,6 @@
 import (
 	"fmt"
 	"os"
-	"syscall"
 	"testing"
 	"sort"
 	. "time"
@@ -17,7 +16,7 @@
 	const delay = int64(100e6)
 	go func() {
 		Sleep(delay / 2)
-		syscall.Kill(os.Getpid(), syscall.SIGCHLD)
+		Interrupt()
 	}()
 	start := Nanoseconds()
 	Sleep(delay)