net: fix TestDialTimeout on windows builder

I don't know what's out there, but something
is answering to 127.0.71.111:80 on our builder,
so use a different port.

Also insert a check that the dial fails, which
would have diagnosed this problem.

Fixes #3016.

R=golang-dev, mikioh.mikioh, r
CC=golang-dev
https://golang.org/cl/5754062

src/pkg/net/dial_test.go

@@ -6,6 +6,7 @@ package net
 
 import (
 	"flag"
+	"fmt"
 	"regexp"
 	"runtime"
 	"testing"
@@ -44,13 +45,22 @@ func TestDialTimeout(t *testing.T) {
 				errc <- err
 			}()
 		}
-	case "darwin":
+	case "darwin", "windows":
 		// At least OS X 10.7 seems to accept any number of
 		// connections, ignoring listen's backlog, so resort
 		// to connecting to a hopefully-dead 127/8 address.
 		// Same for windows.
+		//
+		// Use a bogus port (44444) instead of 80, because
+		// on our 386 builder, this Dial succeeds, connecting
+		// to an IIS web server somewhere.  The data center
+		// or VM or firewall must be stealing the TCP connection.
 		go func() {
-			_, err := DialTimeout("tcp", "127.0.71.111:80", 200*time.Millisecond)
+			c, err := DialTimeout("tcp", "127.0.71.111:44444", 200*time.Millisecond)
+			if err == nil {
+				err = fmt.Errorf("unexpected: connected to %s!", c.RemoteAddr())
+				c.Close()
+			}
 			errc <- err
 		}()
 	default: