test: use T.TempDir to create temporary test directory

The directory created by `T.TempDir` is automatically removed when the
test and all its subtests complete.

Reference: https://pkg.go.dev/testing#T.TempDir
Signed-off-by: Eng Zer Jun <engzerjun@gmail.com>

snapshots/btrfs/btrfs_test.go

@@ -122,18 +122,10 @@ func TestBtrfsMounts(t *testing.T) {
 	ctx := context.Background()
 
 	// create temporary directory for mount point
-	mountPoint, err := os.MkdirTemp("", "containerd-btrfs-test")
-	if err != nil {
-		t.Fatal("could not create mount point for btrfs test", err)
-	}
-	defer os.RemoveAll(mountPoint)
+	mountPoint := t.TempDir()
 	t.Log("temporary mount point created", mountPoint)
 
-	root, err := os.MkdirTemp(mountPoint, "TestBtrfsPrepare-")
-	if err != nil {
-		t.Fatal(err)
-	}
-	defer os.RemoveAll(root)
+	root := t.TempDir()
 
 	b, c, err := boltSnapshotter(t)(ctx, root)
 	if err != nil {