tests: speed up new tests a little

Before: ok  	github.com/rfjakob/gocryptfs/tests/matrix	18.560s
After:  ok  	github.com/rfjakob/gocryptfs/tests/matrix	13.425s

tests/matrix/concurrency_test.go

@@ -26,7 +26,7 @@ func TestConcurrentReadWrite(t *testing.T) {
 	}
 	buf := make([]byte, 100)
 	content := []byte("1234567890")
-	threads := 30
+	threads := 10
 	loops := 30
 	for i := 0; i < threads; i++ {
 		// Reader thread
@@ -80,7 +80,7 @@ func TestConcurrentReadWrite(t *testing.T) {
 func TestConcurrentReadCreate(t *testing.T) {
 	fn := test_helpers.DefaultPlainDir + "/TestConcurrentReadCreate"
 	content := []byte("1234567890")
-	loops := 1000
+	loops := 100
 	var wg sync.WaitGroup
 	// "Creater" thread
 	wg.Add(1)

tests/matrix/matrix_test.go

@@ -151,7 +151,7 @@ func TestWrite10Tight(t *testing.T) {
 	path := test_helpers.DefaultPlainDir + "/TestWrite10Tight"
 	content := make([]byte, 10)
 	buf := make([]byte, 100)
-	for i := 0; i < 1000; i++ {
+	for i := 0; i < 100; i++ {
 		file, err := os.Create(path)
 		if err != nil {
 			t.Fatal(err)