Use plain tox jobs instead of openstack ones
Use plain tox jobs instead of openstack ones

We want to be more flexible in terms of selecting which python versions
we test against. So replace the use of the openstack template with
explicit job invocations.

Change-Id: I2159e81d4a2fd46a83993b01bbea5fb37546ace5

openstack/diskimage-builder,openstack/diskimage-builder