Re-Tool ARMI notebook tests as integration tests

[john-science]

ARMI has two Jupyter Notebook tutorials, used in the docs, that are also run through as unit tests to make sure they still work:

https://github.com/terrapower/armi/blob/abd1db4adfa0c536f9bf9f08f0f1e8b74b1cd0d7/armi/tests/test_notebooks.py#L33

ARMI is a framework, and without external physics kernels it cannot model a reactor. But these two notebooks represent the most external driving of ARMI that you can do without a fully-fledged ARMI application.

Some questions

• Do we need a requirement that we run these notebooks as tests?
• Do we rename this test class ArmiIntegrationTests?
• Do we add more asserts to these tests?