Return list of StepFiles sorted by step from files at path_prefix.

def _read_stepfiles_list(path_prefix, path_suffix=".index", min_steps=0):
  """Return list of StepFiles sorted by step from files at path_prefix."""
  stepfiles = []
  for filename in _try_twice_tf_glob(path_prefix + "*-[0-9]*" + path_suffix):
    basename = filename[:-len(path_suffix)] if path_suffix else filename
    try:
      steps = int(basename.rsplit("-")[-1])
    except ValueError:  # The -[0-9]* part is not an integer.
      continue
    if steps < min_steps:
      continue
    if not os.path.exists(filename):
      tf.logging.info(filename + " was deleted, so skipping it")
      continue
    stepfiles.append(StepFile(basename, os.path.getmtime(filename),
                              os.path.getctime(filename), steps))
  return sorted(stepfiles, key=lambda x: -x.steps)