Skip testing distributed backend if the backend (UCC, NCCL, Gloo) is not available (#98576)
After the recent change on https://github.com/pytorch/pytorch/pull/88110 to add a new c10d test for UCC backend, the test starts to fail on ROCm distributed job. I guess ROCm doesn't support that backend yet, so I go ahead and disable the test there. Please let me know if the support on ROCm is coming, I will close this PR accordingly. But it's now failing in ROCm trunk with `AssertionError: Unknown c10d backend type UCC`, for example https://hud.pytorch.org/pytorch/pytorch/commit/4adba70cc6fa273f210a94a82b337bbddffc3c1d
Pull Request resolved: https://github.com/pytorch/pytorch/pull/98576
Approved by: https://github.com/Fuzzkatt, https://github.com/jithunnair-amd, https://github.com/malfet, https://github.com/ZainRizvi
