Enable the python35 cross jobs for stable/pike g-r changes
Enable the python35 cross jobs for stable/pike g-r changes

We support them for pike and newer, so lets run them to make
sure we don't accidentally break compatibility here.

Change-Id: Ifd50a64721faccaaafd31f75d262ccab1932618c

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