bisect-kit: Fix pylint errors

BUG=b:328778835
TEST=./run_test.sh

Change-Id: I8452a67345b25534e5011d4d7560f1d2f7c9b16b
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/platform/bisect-kit/+/5355417
Reviewed-by: MD Nayeem Jahan Rafi <njrafi@chromium.org>
Commit-Queue: Cheng-Yu Lee <cylee@google.com>
Tested-by: Cheng-Yu Lee <cylee@google.com>
28 files changed