Allow to specify pillar and other Salt dictionaries as builtins,
so flake8 won't complain anymore those names don't exist.
Lint also the .sls #!py files, as they are written in Python too.
This currently needs to use Nasqueron version of arcanist, production branch:
https://github.com/nasqueron/arcanist/commit/15aa482eacd90fdbd238bc8b7a17c4bbba8a0bdd