enable F812 check for flake8
enable F812 check for flake8

The change removes the shadowed variable in list comprehensions and
enables the F812 check

Change-Id: If7b4d6f198795565fe0d8e7524b73555e310cd14
Partial-Bug: 1329017

flavio-fernandes/networking-odl,FedericoRessi/networking-odl,schoksey/networking-odl,schoksey/networking-odl,CiscoSystems/networking-odl,flavio-fernandes/networking-odl,CiscoSystems/networking-odl,mestery/x-stackforge-odl,openstack/networking-odl,openstack/networking-odl,FedericoRessi/networking-odl,openstack/networking-odl