Disable docker-cleanup job when 'testing: true'.

If a container is in a crash loop, when the docker-cleanup script runs, it has a good chance of being removed.

When doing tests, its not uncommon to be in a crash loop scenario while trying to resolve problems, and it is undesirable to have the container removed out from under you.

This is particularly problematic when the container is large and/or the network between you and the registry is not optimal, as one has to repeatedly re-download the container.