[Testing] - Distributing node usecases if possible in BDD

[kozmaz87]

There are multiple scenarios where a distributing node can be very important piece in a puzzle of nodes. It would be nice to have the different types of configurations that make some business sense in some sorts of tests.

[nigelmegitt]

One scenario is:

Push-pull mediator

Each of a set of subtitle authoring or providing nodes needs to make outgoing connections to a stable known location for onward distribution of its output sequence. Each set of subtitle encoders needs to fetch the subtitles from a known stable location. Each providing node makes an outgoing /publish connection to a distributing node. Each encoding/consuming node makes an outgoing '/subscribe` connection to the same distributing node.

One concrete example of this for demonstration purposes is: A User Input Producer web page needs to be a client that makes an outgoing connection to the distributor. A simple consumer is configured to subscribe to a specific single sequence.

Multiple UIPs and consumers (or resequencers or EBU-TT-D encoders) are configured to connect via the same single distributor node.