Update skip pep8 clause to use hacking

Now that projects don't directly use pep8 anymore but rather hacking,
update the ignore pep8 clause to say hacking.

Related patch to ignore hacking in the requirements sync check:
I114b05fb1ec99ec1e0e0162988edb5fa5517df46

Change-Id: Ib21646db18220b40db505856f4796c3d51228abc