Clean up container cache prep in tests
Clean up container cache prep in tests

This patch cleans up the container cache preparation in the tests
due to the following patches:

- https://review.openstack.org/307856 (new image build process)
- https://review.openstack.org/315114 (new apt config process)
- https://review.openstack.org/322188 (new resolver config process)

Change-Id: I2da67e7bec7ad21959edd85e3dc80c97c857fb47

juledwar/openstack-ansible-os_ironic,juledwar/openstack-ansible-os_ironic