'Create a new stack or configure the test to operate on an existing
stack if the environment contains all the necessary IP addresses.'

def setUp(self):

    d = maybeDeferred(super(DockerComposeTests, self).setUp)
    def setup_stack(ignored):
        if (not self._stack_from_environment()):
            return self._new_stack()
    d.addCallback(setup_stack)
    def stack_ready(ignored):
        self.docker_host = (('tcp://' + self.control_node_ip) + ':2376')
        self.addCleanup(self._cleanup_flocker)
    d.addCallback(stack_ready)
    return d
