Docker Container handling for UI tests should be resilient to network issues and honor maven's offline configuration

Currently, network accesses are still attempted while using maven's --offline flag during functional tests. In particular, the test framework tries to pull containers from docker. It should not do this when maven is configured to be offline.

Moreover, the tests fail if these network calls fail (because one is offline).

All this can be worked around by using the offline annotation: `@UITest(offline = true)`

I expect the following:

• tests should not fail because of network issues (which includes the docker registry being down, or working from a train, or during a network failure) if everything needed to run the test is already present (in particlular the docker images)
• network accesses should not be attempted if maven is configured to be offline, regardless the presence of the offline annotation of @UITest