Add ContainerImagePrepare service to CellController role
Add ContainerImagePrepare service to CellController role

The CellController role does not have ContainerImagePrepare
service. This result in empty external_deploy_steps_tasks.yaml
and does not update container images when trying to update
the cell stack.

Change-Id: Ib12d99be11e34b77fe3697c9ce09f84e4a1294f3
Closes-Bug: 1839789

openstack/tripleo-heat-templates,openstack/tripleo-heat-templates