runtime: disable long test (fix arm build)

TBR=r
CC=golang-dev
https://golang.org/cl/4449051
diff --git a/src/pkg/runtime/proc_test.go b/src/pkg/runtime/proc_test.go
index 5caaf69..a15b2d8 100644
--- a/src/pkg/runtime/proc_test.go
+++ b/src/pkg/runtime/proc_test.go
@@ -20,6 +20,10 @@
 }
 
 func TestStopTheWorldDeadlock(t *testing.T) {
+	if testing.Short() {
+		t.Logf("skipping during short test")
+		return
+	}
 	runtime.GOMAXPROCS(3)
 	compl := make(chan int, 1)
 	go func() {