Removing getMasterCs from getMicroSuffix

[john-science]

Description

In reference to Issue #930, this is a minor rewrite of getMicroSuffix() intended to help us remove one of the last 6 calls to getMasterCs() in ARMI.

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Checklist

• This PR has only one purpose or idea.
• Tests have been added/updated to verify that the new/changed code works.

• The code style follows good practices.
• The commit message(s) follow good practices.

• The release notes (location doc/release/0.X.rst) are up-to-date with any bug fixes or new features.
• The documentation is still up-to-date in the doc folder.
• The dependencies are still up-to-date in setup.py.

[john-science]

@opotowsky I don't see any reason this would affect our downstream projects. But I have not tested it thoroughly downstream, yet.

[john-science]

Okay, I added a unit test to cover the three major cases in getMicroSuffix(). And that fixed the code coverage problem.

[opotowsky]

@opotowsky I don't see any reason this would affect our downstream projects. But I have not tested it thoroughly downstream, yet.

I also don't see any reason it would impact anything. I'll be on the lookout, but don't see any reason to not merge once approved