Add `rdma_mpi` to test suite

[sbryngelson]

Add rdma_mpi = 'T' to test suite. This only gets turned on in OpenACC (GPU) mode, which only exists on the Phoenix GPU runner and the Frontier runner, both of which support it.

Note: There needs to be a way to skip this test if the compiler does not support it (in non-CI cases).

[sbryngelson]

One option: add --rdma to ./mfc.sh test as an optional flag that adds RDMA tests and is used in CI, but is off by default.

Or, per @henryleberre suggestion: ./mfc.sh test --gpu -- -c frontier -- --rdma which passes to ./mfc.sh run directly rather than relying on the test suite to support this functionality.

[aricer123]

"Add rdma_mpi = 'T' to test suite" I'm a little confused by what this means.
So far, I have created a flag for test that passes to run provided that we are running on a gpu/gpu mode.
Is there a feature already that runs RDMA tests if an --rdma flag is set in run? What work has been done with this feature so far and what more do I need to implement?

[sbryngelson]

Is there a feature already that runs RDMA tests if an --rdma flag is set in run?

No, it is set in the case.py file. This (currently nonexistent) flag, or something like it, would have to be added so turning on this feature could also be controlled from the command line.