Use py36 instead of py35 for periodic master jobs
Use py36 instead of py35 for periodic master jobs

OpenStack Train will test on py36 instead of py35, change the periodic
master jobs periodic-jobs-with-X-master to use py36.

Depends-On: https://review.opendev.org/654571
Change-Id: Ic5396e84b8593de464367b7e75376e5ec702dd96

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