post install task is broken with Slurm + hybrid engine

[KADichev]

After doing

srun -p TaiShanV110  -c 64 -t 08:00:00 --pty /bin/bash
< load Spack environment>
make 
make install

post install tasks in make install are broken for hybrid engine, as follows:

[anyzelman]

On the hybrid postinstall checks specifically: the slurm srun command should ask for (at least 3) tasks. (My last couple of SLURM allocations when I was testing LPF even used 10 tasks -- I think one or two functional tests require that)

Generally: did you export HYDRA_BOOTSTRAP=ssh if MPICH or the other workaround for if OpenMPI? (The slurm deadlock issue on our cluster is not resolved right?) I'm hesitant to acknowledge these as LPF bugs because our cluster's SLURM has been misbehaving-- it's hard / impossible to isolate where the error comes from at present while no errors occur on the other systems tested on.