MPI launch error when using shell scheduler

[BerengerBerthoul]

With Intel MPI and scheduler=shell, it seems that the MPI processes in a step can't be launched concurrently and fail with this error :

f01.1629534PSM2 can't open hfi unit: 0 (err=23)
Abort(1615247) on node 0 (rank 0 in comm 0): Fatal error in PMPI_Init_thread: Other MPI error, error stack:
MPIR_Init_thread(178)........: 
MPID_Init(1532)..............: 
MPIDI_OFI_mpi_init_hook(1552): 
create_vni_context(2131).....: OFI endpoint open failed (ofi_init.c:2131:create_vni_context:Invalid argument)

Using n-worker strictly less than the number of cores seems to solve the issue