[torch/elastic] Fix the agent store key prefix used by workers (#61590)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/61590
This PR fixes the bug where the state of the first run of a failed training job leaks to the secondary runs due to constant worker key prefix.
ghstack-source-id: 133494239
Test Plan: Run the existing integ tests.
Reviewed By: SciPioneer
Differential Revision: D29682743
fbshipit-source-id: d96ecadcfe5b6563225ee19f5d0776c7f935393a
