Exclude heat-cfn, heat-watch from pep8

They are due for removal in https://review.openstack.org/#/c/38228/
and are causing many H233 errors when using the syncronised
requirements versions.

Change-Id: Ie632de44360519a0f705052ebaf4fe1304a0c290
Merge "Exclude heat-cfn, heat-watch from pep8"