The current pylint is very old at this point.  Pull in the latest version
as it supports a lot more features.  Also need to fix the pylint wrapper
to actually update sys.path to use the local modules.

We include the six module since not all bots have it, and it's small.

This will trigger new warnings in files, but they look like legitimate
issues that should be fixed at some point.

BUG=chromium:431514
TEST=ran on some code bases and checked output

Review URL: https://codereview.chromium.org/741503002

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@292988 0039d316-1c4b-4281-b951-d872f2087c98