cmd/dist: increase timeout scale to 3 for windows

cmd/go can sometimes take up to 400s on windows due
to various issues (disk I/O on builders being the
latest cause). Increase the timeout scale to account
for this.

Change-Id: I1fd4964472a70fb0f33cf6ed73298c034b9c1fb0
Reviewed-on: https://go-review.googlesource.com/120762
Run-TryBot: Andrew Bonventre <[email protected]>
Reviewed-by: Brad Fitzpatrick <[email protected]>
TryBot-Result: Gobot Gobot <[email protected]>

Author: andybons

src/cmd/dist/test.go

@@ -308,7 +308,7 @@ func (t *tester) registerStdTest(pkg string) {
 			timeoutSec := 180
 			for _, pkg := range stdMatches {
 				if pkg == "cmd/go" {
-					timeoutSec *= 2
+					timeoutSec *= 3
 					break
 				}
 			}