code: static List<File> listRootAndExtensionDirectories() {
          List<File> dirs = listExtensionDirectories();
          dirs.add(0, new File(CustomUtils.getInstallRoot())); // place wlp first.
          return dirs;
      }
docs: Returns the list of the absolute path of the product root and extension directories.
  The directory may or may not exist.
  the list of directories which this method returns is:
  1. wlp/
  2. wlp/usr/extension/
  3. all locations returned from ProductExtension.getProductExtensions()