Document E125 as a won't fix.

As per the discussion in https://review.openstack.org/#/c/36788/ the
tempest team does not want to use E125 until
https://github.com/jcrocholl/pep8/issues/126 is  resolved.

Change-Id: I124e6f14db81d030a470ef3e73a33b15e9dea9ef
Merge "Document E125 as a won't fix."