Ensure ATS can run CPU and GPU jobs concurrently on the same node with Flux

[dawson6]

Verify (and fix if not verified) that we can

1. Run CPU only tests and CPU+GPU tests on the same node concurrently using flux.

This may mean creating (or tweaking) an existing test setup such that two codes are specified in the ATS test files.

That is

Code A) built for the CPU only. Does not need access to the GPU at all (in particularly for memory access)
Code B) Built for the CPU+GPU. That is it will require access to either hipMalloc or hipMallocManaged memory at run time.

Verify we can saturate the nodes (for throughput) with a combination of the above codes.