allow the build of specific overlays

internal/app/wwctl/overlay/build/root.go

@@ -10,13 +10,16 @@ var (
 		Long:                  "This command builds overlays for given nodes.",
 		RunE:                  CobraRunE,
 	}
-	BuildHost  bool
-	BuildNodes bool
+	BuildHost   bool
+	BuildNodes  bool
+	OverlayName string
 )
 
 func init() {
 	baseCmd.PersistentFlags().BoolVarP(&BuildHost, "host", "H", false, "Build overlays only for the host")
 	baseCmd.PersistentFlags().BoolVarP(&BuildNodes, "nodes", "N", false, "Build overlays only for the nodes")
+	baseCmd.PersistentFlags().StringVarP(&OverlayName, "overlay", "o", "", "Build only specific overlay")
+
 }
 
 // GetRootCommand returns the root cobra.Command for the application.