net: don't block forever in splice test cleanup on failure

The ppc64x builders are failing on the new splice test from CL 113997
but the actual failure is being obscured by a test deadlock.

Change-Id: I7747f88bcdba9776a3c0d2f5066cfec572706108
Reviewed-on: https://go-review.googlesource.com/133417
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>
Reviewed-by: Tobias Klauser <tobias.klauser@gmail.com>

src/net/splice_test.go

@@ -15,6 +15,7 @@ import (
 	"strconv"
 	"sync"
 	"testing"
+	"time"
 )
 
 func TestSplice(t *testing.T) {
@@ -332,7 +333,19 @@ func startSpliceClient(conn Conn, op string, chunkSize, totalSize int) (func(),
 		close(donec)
 	}()
 
-	return func() { <-donec }, nil
+	return func() {
+		select {
+		case <-donec:
+		case <-time.After(5 * time.Second):
+			log.Printf("killing splice client after 5 second shutdown timeout")
+			cmd.Process.Kill()
+			select {
+			case <-donec:
+			case <-time.After(5 * time.Second):
+				log.Printf("splice client didn't die after 10 seconds")
+			}
+		}
+	}, nil
 }
 
 func init() {