Allow disable of W601

While has_key no longer exists for python 3, there are still libraries
which have this method and do not allow for 'key in dict'. This enables
the "nopep8/noqa" methods of disabling the warning per-line.

Signed-off-by: Sol Jerome <sol.jerome@gmail.com>
Merge pull request #227 from solj/disable-w601

Allow disable of W601