update wording around pep8 exceptions
update wording around pep8 exceptions

At least once a cycle we get contributions from new folks that attempt
to update a bunch of pep8 formatting. They believe that this is in
good faith helping, but don't realize we really aren't likely to
accept that.

Update the text here to explain that more clearly, so that people
don't keep falling down this rabbit hole.

Change-Id: Iec383a18cb3d64b9655e5bd1d82cabd3e785686c

rahulunair/nova,klmitch/nova,gooddata/openstack-nova,mikalstill/nova,cloudbase/nova,jianghuaw/nova,jianghuaw/nova,vmturbo/nova,Juniper/nova,Juniper/nova,Juniper/nova,alaski/nova,vmturbo/nova,gooddata/openstack-nova,rahulunair/nova,vmturbo/nova,phenoxim/nova,rajalokan/nova,rajalokan/nova,mikalstill/nova,rahulunair/nova,openstack/nova,hanlind/nova,mahak/nova,rajalokan/nova,openstack/nova,mikalstill/nova,sebrandon1/nova,cloudbase/nova,phenoxim/nova,rajalokan/nova,jianghuaw/nova,Juniper/nova,sebrandon1/nova,vmturbo/nova,hanlind/nova,klmitch/nova,mahak/nova,hanlind/nova,alaski/nova,klmitch/nova,gooddata/openstack-nova,jianghuaw/nova,gooddata/openstack-nova,mahak/nova,klmitch/nova,sebrandon1/nova,cloudbase/nova,openstack/nova