Rework aux_cmeps test list

The aux_cmeps test list has fallen into disuse and there are numerous failing tests. We should rework it.

See also https://github.com/ESCOMP/CESM/issues/356

We need to do some broader thinking at some point regarding how to define this test suite. There is a tension between (1) getting full coverage, (2) keeping the test suite manageable in size, and (3) making the test suite runnable across multiple systems (CESM, NorESM, etc.). We can consider using X compsets for some of this. The picture will also change when we eventually split CMEPS into (a) the shared mediator, and (b) the CESM-specific driver (as @mvertens has been suggesting): at that point, each of those could have its own test suite that is suited for what is contained in that repository.