refactored overlay class

overlay.GetOverlay(name) returns now an error if the overlay doesn't
exist. This is the most canonical way to act if there is no overlay.

internal/app/wwctl/overlay/mkdir/main.go

@@ -1,36 +1,15 @@
 package mkdir
 
 import (
-	"fmt"
-	"os"
-
 	"github.com/spf13/cobra"
 	"github.com/warewulf/warewulf/internal/pkg/overlay"
-	"github.com/warewulf/warewulf/internal/pkg/wwlog"
 )
 
 func CobraRunE(cmd *cobra.Command, args []string) (err error) {
-	overlayName := args[0]
-	dirName := args[1]
 
-	overlay_ := overlay.GetOverlay(overlayName)
-	if !overlay_.IsSiteOverlay() {
-		overlay_, err = overlay_.CloneSiteOverlay()
-		if err != nil {
-			return err
-		}
-	}
-
-	if !overlay_.Exists() {
-		return fmt.Errorf("overlay does not exist: %s", overlayName)
-	}
-
-	overlayDir := overlay_.File(dirName)
-	wwlog.Debug("Will create directory in overlay: %s:%s", overlayName, dirName)
-	err = os.MkdirAll(overlayDir, os.FileMode(PermMode))
+	myOverlay, err := overlay.GetOverlay(args[0])
 	if err != nil {
-		return fmt.Errorf("could not create directory: %s", overlayDir)
+		return err
 	}
-
-	return nil
+	return myOverlay.Mkdir(args[1], PermMode)
 }