tox: add both py35 and py36 to test whichever is available
tox: add both py35 and py36 to test whichever is available

Signed-off-by: Alfredo Deza <3f4d00ffa77e6441ab2d23c25a618925d2383b02@redhat.com>

ceph/ceph-deploy,ceph/ceph-deploy