Add '--allow-run-as-root' to mpiexec to allow running distributed test inside a container (#43794)
Summary:
Inside a container, the user is often root. We should allow this use case so that people can easily run `run_test.py` insider a container
Pull Request resolved: https://github.com/pytorch/pytorch/pull/43794
Reviewed By: ezyang
Differential Revision: D24904469
Pulled By: malfet
fbshipit-source-id: f96cb9dda3e7bd18b29801cde4c5b0616c750016
