net: do not test TestReadWriteDeadline timeout upper bound during short test

It also increases timeout deltas to allow for longer wait.
Also disables this test on plan9.

R=golang-dev, minux.ma
CC=golang-dev
https://golang.org/cl/6821062

src/pkg/net/ipsock_plan9.go

@@ -24,6 +24,8 @@ func probeIPv6Stack() (supportsIPv6, supportsIPv4map bool) {
 	return false, false
 }
 
+var canCancelIO = true // used for testing current package
+
 // parsePlan9Addr parses address of the form [ip!]port (e.g. 127.0.0.1!80).
 func parsePlan9Addr(s string) (ip IP, iport int, err error) {
 	addr := IPv4zero // address contains port only

src/pkg/net/timeout_test.go

@@ -148,19 +148,24 @@ func TestTimeoutAccept(t *testing.T) {
 }
 
 func TestReadWriteDeadline(t *testing.T) {
+	switch runtime.GOOS {
+	case "plan9":
+		t.Logf("skipping test on %q", runtime.GOOS)
+		return
+	}
+
 	if !canCancelIO {
 		t.Logf("skipping test on this system")
 		return
 	}
 	const (
-		readTimeout  = 100 * time.Millisecond
-		writeTimeout = 200 * time.Millisecond
-		delta        = 40 * time.Millisecond
+		readTimeout  = 50 * time.Millisecond
+		writeTimeout = 250 * time.Millisecond
 	)
 	checkTimeout := func(command string, start time.Time, should time.Duration) {
 		is := time.Now().Sub(start)
 		d := should - is
-		if d < -delta || delta < d {
+		if d < -30*time.Millisecond || !testing.Short() && 150*time.Millisecond < d {
 			t.Errorf("%s timeout test failed: is=%v should=%v\n", command, is, should)
 		}
 	}