docs: def image_get_root_disk_size(self, image_name):
          """Get the root disk size of the image
  
          :param image_name: the image name in image Repository
          :returns: the disk size in units CYL or BLK
          """
          try:
              return self._imageops.image_get_root_disk_size(image_name)
          except exception.SDKBaseException:
              LOG.error("Failed to get root disk size units of image '%s'" %
                        image_name)
              raise