Rework aux_cmeps test list

[billsacks]

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

See also ESCOMP/CESM#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.

[ekluzek]

The thing that we want to exercise in testing CMEPS are all the different driver options, different types of prognostic compsets, and the different configurations of fields that can be passed between components. We've done some of that by having component specific compsets/tests in aux_cmeps, but then they are closely tied to those specific components. With X compsets, we should be able to have compsets that mimic standard compsets like: fully active, land-only, atm/lnd/ice-only, ocean/ice-only, rof/glc-only etc. Then the testing could be indepenent of the ESM, but still do similar configurations to each ESM. And it would be good to have testmods in CMEPS that are focussed on exercising the CMEPS options.