Per suggestion by @bangerth, allow mpirun to execute as root if two
envars are set to specific values
Per conversation with @jsquyres, name the envars OMPI_ALLOW_RUN_AS_ROOT
and OMPI_ALLOW_RUN_AS_ROOT_CONFIRM
Fixes#4451
Signed-off-by: Ralph Castain <rhc@open-mpi.org>
Signed-off-by: Jeff Squyres <jsquyres@cisco.com>
(cherry picked from commit 7f1444d5f9e504ff50392a0f73e81787c01b7a0e)