time: Sleep does better job then runtime.Gosched in TestAfterStress
time: Sleep does better job then runtime.Gosched in TestAfterStress

for slow windows-386 builder

R=golang-dev, dave, rsc
CC=golang-dev
https://codereview.appspot.com/7128053
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go