drivers/graphtest: remove temp dirs in case of errors

In the default ('go test'), the /tmp/ is typically not on btrfs, and
running the test leaves the temp dirs in place.

Signed-off-by: Han-Wen Nienhuys <[email protected]>

drivers/graphtest/graphtest_unix.go

@@ -47,6 +47,8 @@ func newGraphDriver(t testing.TB, name string, options []string, root string, ru
 	d, err := graphdriver.GetDriver(name, graphdriver.Options{DriverOptions: options, Root: root, RunRoot: runroot})
 	if err != nil {
 		t.Logf("graphdriver: %v\n", err)
+		os.RemoveAll(runroot)
+		os.RemoveAll(root)
 		if errors.Is(err, graphdriver.ErrNotSupported) || errors.Is(err, graphdriver.ErrPrerequisites) || errors.Is(err, graphdriver.ErrIncompatibleFS) {
 			t.Skipf("Driver %s not supported", name)
 		}