runtime: disable TestGoroutineParallelism on uniprocessor

It's a bad test and it's worst on uniprocessors.

Fixes #11143.

Change-Id: I0164231ada294788d7eec251a2fc33e02a26c13b
Reviewed-on: https://go-review.googlesource.com/12522Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>

src/runtime/proc_test.go

@@ -96,6 +96,10 @@ func TestYieldLocked(t *testing.T) {
 }
 
 func TestGoroutineParallelism(t *testing.T) {
+	if runtime.NumCPU() == 1 {
+		// Takes too long, too easy to deadlock, etc.
+		t.Skip("skipping on uniprocessor")
+	}
 	P := 4
 	N := 10
 	if testing.Short() {