Exporting port bindings fails if EnvInvisibleAction does not contain Port bindings

bd510236b553a6158d16babfb83d4913e5637f46 broke variable resolution for DOCKER_CONTAINER_IDS:
Create a Job with steps
* _Create container_
* _Start container_ using $DOCKER_CONTAINER_IDS
The build will fail with 

> Failed to execute Docker command Start container(s): No such container $DOCKER_CONTAINER_IDS

Reason: The first step creates an action without port bindings. The second step then fails silently with an NPE when creating the port binding environment variables. The code to add DOCKER_CONTAINER_IDS is not executed.