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:

armi/armi/tests/test_notebooks.py

Line 33 in abd1db4

class NotebookTests(unittest.TestCase):

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?