Add a LILAC test with threading turned on

We should probably have at least one LILAC test where threading is turned on, to ensure that the LILAC build and run works with threading. I don't think we need to go so far as to introduce an equivalent of a PET test (i.e., comparing answers with and without threading), but I do think we should have a smoke test that is built and run with threading.

This will require adding a bit of logic in the LILAC system test code: if the parent test case has threading, then we will need to set the flag `--build-with-openmp`.

We should then manually examine the log file output from CTSM in this LILAC test to ensure that it is actually being run with threading, with the expected number of threads (because I'm not positive that the threading information will propagate through from CIME properly).