Update Windows runtime to use snapshotter and differ layers

This changes the Windows runtime to use the snapshotter and differ
created layers, and updates the ctr commands to use the snapshotter and differ.

Signed-off-by: Darren Stahl <darst@microsoft.com>

mount/mount_windows.go

@@ -39,11 +39,6 @@ func (m *Mount) Mount(target string) error {
 	if err = hcsshim.PrepareLayer(di, layerID, parentLayerPaths); err != nil {
 		return errors.Wrapf(err, "failed to prepare layer %s", m.Source)
 	}
-	defer func() {
-		if err != nil {
-			hcsshim.UnprepareLayer(di, layerID)
-		}
-	}()
 	return nil
 }
 
@@ -67,10 +62,12 @@ func (m *Mount) GetParentPaths() ([]string, error) {
 
 // Unmount the mount at the provided path
 func Unmount(mount string, flags int) error {
-	home, layerID := filepath.Split(mount)
-	var di = hcsshim.DriverInfo{
-		HomeDir: home,
-	}
+	var (
+		home, layerID = filepath.Split(mount)
+		di            = hcsshim.DriverInfo{
+			HomeDir: home,
+		}
+	)
 
 	if err := hcsshim.UnprepareLayer(di, layerID); err != nil {
 		return errors.Wrapf(err, "failed to unprepare layer %s", mount)