runtime/race: ignore user GORACE env var in tests

I did 'export GORACE=atexit_sleep_ms=0' in a console
and then was puzzled as to why race tests fail.
Existing GORACE env var may (or may not) override
the one that we setup.
Filter out GORACE as we do for other important env vars.

Change-Id: I29be86b0cbb9b5dc7f9efb15729ade86fc79b0e0
Reviewed-on: https://go-review.googlesource.com/32163Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

src/runtime/race/race_test.go

@@ -154,7 +154,9 @@ func runTests(t *testing.T) ([]byte, error) {
 	// It is required because the tests contain a lot of data races on the same addresses
 	// (the tests are simple and the memory is constantly reused).
 	for _, env := range os.Environ() {
-		if strings.HasPrefix(env, "GOMAXPROCS=") || strings.HasPrefix(env, "GODEBUG=") {
+		if strings.HasPrefix(env, "GOMAXPROCS=") ||
+			strings.HasPrefix(env, "GODEBUG=") ||
+			strings.HasPrefix(env, "GORACE=") {
 			continue
 		}
 		cmd.Env = append(cmd.Env, env)