Add py3.5 support in setup.cfg
Add py3.5 support in setup.cfg

As defined in https://governance.openstack.org/tc/goals/pike/python35.html
Pike community goal for py35, adding py35 to setup.cfg.

Change-Id: I8fd5e405c24e7e7072d0bfa1defda11fdbe56e53

openstack-dev/hacking,openstack-dev/hacking