net/http: updated bundled http2 copy, enable some tests

Updates bundled copy of x/net/http2 to include
https://golang.org/cl/17823 (catching panics in Handlers)

Fixes #13555

Change-Id: I08e4e38e736a8d93f5ec200e8041c143fc6eafce
Reviewed-on: https://go-review.googlesource.com/17824
Reviewed-by: Ian Lance Taylor <[email protected]>
Run-TryBot: Brad Fitzpatrick <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: bradfitz

src/net/http/h2_bundle.go

@@ -1926,16 +1926,12 @@ func testZeroLengthPostAndResponse(t *testing.T, h2 bool) {
 }
 
 func TestHandlerPanicNil_h1(t *testing.T) { testHandlerPanic(t, false, h1Mode, nil) }
-func TestHandlerPanicNil_h2(t *testing.T) {
-	t.Skip("known failure; golang.org/issue/13555")
-	testHandlerPanic(t, false, h2Mode, nil)
-}
+func TestHandlerPanicNil_h2(t *testing.T) { testHandlerPanic(t, false, h2Mode, nil) }
 
 func TestHandlerPanic_h1(t *testing.T) {
 	testHandlerPanic(t, false, h1Mode, "intentional death for testing")
 }
 func TestHandlerPanic_h2(t *testing.T) {
-	t.Skip("known failure; golang.org/issue/13555")
 	testHandlerPanic(t, false, h2Mode, "intentional death for testing")
 }