add elastic zeus handler (#16746)
Summary:
Pull Request resolved: https://github.com/pytorch/pytorch/pull/16746
as titled. We use a special url schem elasticzeus for elastic zeus so that we dont need to change the public interface of init_process_group.
Reviewed By: aazzolini, soumith
Differential Revision: D13948151
fbshipit-source-id: 88939dcfa0ad93467dabedad6905ec32e6ec60e6
