tests: Fix rare test crash (#4175)

Fix rare test crash by improving the randomness logic.

cmd/test-utils_test.go

@@ -2361,3 +2361,28 @@ func getEndpointsLocalAddr(endpoints EndpointList) string {
 
 	return globalMinioHost + ":" + globalMinioPort
 }
+
+// fetches a random number between range min-max.
+func getRandomRange(min, max int, seed int64) int {
+	// special value -1 means no explicit seeding.
+	if seed != -1 {
+		rand.Seed(seed)
+	}
+	return rand.Intn(max-min) + min
+}
+
+// Randomizes the order of bytes in the byte array
+// using Knuth Fisher-Yates shuffle algorithm.
+func randomizeBytes(s []byte, seed int64) []byte {
+	// special value -1 means no explicit seeding.
+	if seed != -1 {
+		rand.Seed(seed)
+	}
+	n := len(s)
+	var j int
+	for i := 0; i < n-1; i++ {
+		j = i + rand.Intn(n-i)
+		s[i], s[j] = s[j], s[i]
+	}
+	return s
+}