Enforce pylint on payload_utils.

- Skipping proto_converters for now.

BUG=chromium:1092516
TEST=CQ
TEST=repo upload outside chroot
TEST=repo upload inside chroot

Change-Id: I1263731c8425d6ba143e669b13de1eb909971935
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/config/+/2236575
Commit-Queue: Andrew Lamb <andrewlamb@chromium.org>
Tested-by: Andrew Lamb <andrewlamb@chromium.org>
Reviewed-by: Sean McAllister <smcallis@google.com>
diff --git a/payload_utils/checker/io_utils_test.py b/payload_utils/checker/io_utils_test.py
index 35aea1a..09ba58b 100644
--- a/payload_utils/checker/io_utils_test.py
+++ b/payload_utils/checker/io_utils_test.py
@@ -9,13 +9,13 @@
 import tempfile
 import unittest
 
+from google.protobuf import json_format
+
 from checker import io_utils
 
 from chromiumos.config.payload.config_bundle_pb2 import ConfigBundle
 from chromiumos.config.api.program_pb2 import ProgramList, Program
 
-from google.protobuf import json_format
-
 
 class IoUtilsTest(unittest.TestCase):
   """Tests for io_utils."""