Use python3 for translation jobs
Use python3 for translation jobs

Horizon no longer support python2 as it has dropped Django 1.11
support which is the last version with python 2.7 support.
However, the translation jobs still require python2, so the translation
jobs are failing after horizon dropped python2 support.
It is time to ensure python3 in the translation jobs.

Change-Id: Id78484bf5366601b11547e80b772a0eec03622d0

openstack-infra/project-config,openstack-infra/project-config