Unify testutil.Unmount on Windows and Unix

Signed-off-by: Paul "TBBle" Hampson <Paul.Hampson@Pobox.com>

pkg/testutil/helpers.go

@@ -23,6 +23,9 @@ import (
 	"path/filepath"
 	"strconv"
 	"testing"
+
+	"github.com/containerd/containerd/mount"
+	"github.com/stretchr/testify/assert"
 )
 
 var rootEnabled bool
@@ -79,3 +82,10 @@ func DumpDirOnFailure(t *testing.T, root string) {
 		DumpDir(t, root)
 	}
 }
+
+// Unmount unmounts a given mountPoint and sets t.Error if it fails
+func Unmount(t testing.TB, mountPoint string) {
+	t.Log("unmount", mountPoint)
+	err := mount.UnmountAll(mountPoint, umountflags)
+	assert.NoError(t, err)
+}