PyLint integration in Arcanist hardcodes flags to pylint: https://secure.phabricator.com/diffusion/ARC/browse/master/src/lint/linter/ArcanistPyLintLinter.php;f099168aa82c1c1f5a6fd8f8b8f32e9237e7b309$165.
The problem is that in newer versions of pylint, -i flag does not exist anymore. People running easy_install pylint as per arcanist recommendation will get the newest version which is not supported.
Please make arcanist support newer pylint versions. Note that newer pylint versions might have the output formating changed also.