[Torchelasic] Create root log directory by default (#121257)
Summary:
After refactoring in https://github.com/pytorch/pytorch/pull/120691, default behavior unintentionally was changes from creating tempdir for logging to not capturing any logs by torch Elastic Agent.
Reverting the behavior to:
- making tempdir when log dir is not specified
- allowing non-empty root log dir
- Note: in case attempt folder exists, it will be pruned here: https://github.com/pytorch/pytorch/blob/main/torch/distributed/elastic/multiprocessing/api.py#L294
Differential Revision: D54531851
Pull Request resolved: https://github.com/pytorch/pytorch/pull/121257
Approved by: https://github.com/d4l3k
