build-namelist tester wasn't properly going over all use-cases

[ekluzek]

Brief summary of bug

As a contributor to #2492, the build-namelist unit tester wasn't going over all the use-cases like it was supposed to.

General bug information

CTSM version you are using: ctsm5.2.002

Does this bug cause significantly incorrect results in the model's science? No

Configurations affected: Just the unit-tester itself

Details of bug

I think this bug goes way back. I had been relying on the fact that all use-cases were tested at least in the unit-tester and that wasn't happening. As part of the fix I'll add an update that makes sure the number of use-cases are as expected.