math/rand: decrease test duration in short mode

TestNonStandardNormalValues runs 1.5s,
the change reduces it to 0.2s in short mode.
The problem is with slow machines, emulators and dynamic tools.

R=golang-dev, r
CC=golang-dev
https://golang.org/cl/5540065

src/pkg/math/rand/rand_test.go

@@ -131,8 +131,14 @@ func TestStandardNormalValues(t *testing.T) {
 }
 
 func TestNonStandardNormalValues(t *testing.T) {
-	for sd := 0.5; sd < 1000; sd *= 2 {
-		for m := 0.5; m < 1000; m *= 2 {
+	sdmax := 1000.0
+	mmax := 1000.0
+	if testing.Short() {
+		sdmax = 5
+		mmax = 5
+	}
+	for sd := 0.5; sd < sdmax; sd *= 2 {
+		for m := 0.5; m < mmax; m *= 2 {
 			for _, seed := range testSeeds {
 				testNormalDistribution(t, numTestSamples, m, sd, seed)
 			}