Update docker support for Nemo/Nccl testing

[amaslenn]

Summary

1. Update docker support for Nemo/Nccl testing
2. This PR depends on Flat tests structure, fix warnings #17.

Test Plan

1. Test by @amaslenn
CI
2. Test by @TaekyungHeo
2.1 Slurm command generation for a given URL

  [cmd_args.docker_image_url]
  type = "str"
  default = [URL]

$ cloudaix --mode dry-run --system_config_path ... --test_scenario_path conf/v0.6/general/test_scenario/nemo_launcher.toml 

... container=**[installed_docker_image_path]**

2.1 Slurm command generation for a given path

  [cmd_args.docker_image_url]
  type = "str"
  default = [local_file_path]

$ cloudaix --mode dry-run --system_config_path ...--test_scenario_path conf/v0.6/general/test_scenario/nemo_launcher.toml 

... container=[local_file_path]

Additional Notes

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