Fix Jenkins translation jobs
Fix Jenkins translation jobs

The job neutron-propose-translation-update
does not update from
transifex since our po files contain duplicate entries where
obsolete entries duplicate normal entries.

Remove all obsolete entries to fix the job.

Add test to pep8 that checks that no new breakages get
introduced.

Change-Id: I9c680eeefecfa124c5b2900b7fa7a0a8f7e8ebd6
Closes-Bug: #1299349

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