I've observed the following things about locations of spawned
processes by running a simple program, please correct me if anything
1. the default policy seems to be byslot, and specifying bynode in
mpirun command line can change that.
2. the order of hosts in the hostfile is used, and the order specified
in the MPI_Info("host") ignored.
3. when the policy is byslot, slots occupied by parent processes seem
to be ignored.
I.e. locations of spawned processes are determined in the same way as
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