As above, if ``timeout`` is a class/instance variable, then here we can initialize ``timeout = self.subtest.config['docker_timeout']``.  In the other interface classes, we can decide how to bring in a timeout value if it needs to default differently.  Yeah, I think this would be good to have as a class/instance variable.  It's okay to define it in ``DockerImagesBase`` and leave it "floating", or it could maybe be an optional param to ``__init__``, either way is fine.