docs: def _get_image_size(self, image_path):
          """Return disk size in bytes"""
          command = 'du -b %s' % image_path
          (rc, output) = zvmutils.execute(command)
          if rc:
              msg = ("Error happened when executing command du -b with"
                     "reason: %s" % output)
              LOG.error(msg)
              raise exception.SDKImageOperationError(rs=8)
          size = output.split()[0]
          return size