PR #12439: [GPU] Multinode support for multihost_hlo_runner
PR #12439: [GPU] Multinode support for multihost_hlo_runner

Imported from GitHub PR https://github.com/openxla/xla/pull/12439

This PR adds multinode support to the multihost_hlo_runner. To use, there is a new command line argument `address` for the address of the coordinator/root node.

Example usage with SLURM:
```
bazel run //xla/tools/multihost_hlo_runner:hlo_runner_main -- \
  --task_id=${SLURM_PROCID} \
  --num_nodes=${SLURM_NTASKS} \
  --address="${SLURM_LAUNCH_NODE_IPADDR}:12345" \
  ...
  ```
Copybara import of the project:

--
ad1705053185c32abbf4d917f2b1fd669d5b6893 by Trevor Morris <tmorris@nvidia.com>:

Multinode changes for hlo_runner_main

Merging this change closes #12439

FUTURE_COPYBARA_INTEGRATE_REVIEW=https://github.com/openxla/xla/pull/12439 from trevor-m:tmorris-multinode-runner ad1705053185c32abbf4d917f2b1fd669d5b6893
