[TASK] Multinode Test Harness w/ Dynamic add/drop support

[tbraun96]

Our test harness currently works for N=1 nodes. For testing blueprints that only need 1 node, what we currently have works well and follows a composable design (as opposed to a "black box" design we use to have).

Now, we need to get N=n nodes working. The same composability should still apply, and should be reverse-compatible with existing tests to not cause interruption.

Additionally, we should add the ability to add and drop nodes on command.