Add automatic detection of hetero nodes

Users are having a hard time adjusting to the --hetero-nodes option, so add a short topology "signature" to the orted cmd line so they can compare it to their local topology and return a topo if theirs differs from that found by mpirun.

Based on master commits:
open-mpi/ompi@bb529eb
open-mpi/ompi@9b2f8cd
open-mpi/ompi@18d9fdf

@jsquyres see what you think