Log out and possibly reraise errors during import.

def _handle_errors(errors):
  """Log out and possibly reraise errors during import."""
  if not errors:
    return
  log_all = True  # pylint: disable=unused-variable
  err_msg = "T2T: skipped importing {num_missing} data_generators modules."
  print(err_msg.format(num_missing=len(errors)))
  for module, err in errors:
    err_str = str(err)
    if not _is_import_err_msg(err_str, module):
      print("From module %s" % module)
      raise err
    if log_all:
      print("Did not import module: %s; Cause: %s" % (module, err_str))