Test model tweaks

[mabruzzo]

This makes 2 largely superficial tweaks (in 2 commits) to the example scripts that invoked by test_model.py

1. The first commit makes it possible to disable plot generation¹
2. The second commit adds a simple command line interface to each of the tests. This makes it easier to query what the different parameter sets and input sets mean when you want to debug a failing test.

These are all superficial changes (the tests themselves are not impacted at all). Now that I finished making these changes I realized that they don't do a ton. But I think they are still worth including since they make debugging a little more ergonomic.

Footnotes

1. Originally, I mistakenly believed that the plotting logic was dominating the time it takes to run a test and so I disabled plot- any time one of the examples was run as part of the test suite. In the second commit, I re-enabled plot-generation when run as part of the test suite. ↩