Set OMP_NUM_THREADS in batch script

[marcelo-alvarez]

Modification to ensure that the line export OMP_NUM_THREADS=threads_per_core is added to automatically generated batch scripts, where threads_per_core is the argument to the -c flag in the srun command.

Currently, this is not the case, and consequently the number of threads being used in #pragma omp parallel regions of compiled C++ code is currently being set to whatever the value of OMP_NUM_THREADS is when the batch script is submitted in (e.g., OMP_NUM_THREADS=1 after running source /global/common/software/desi/desi_environment.sh master on cori).

Please verify that this change results in the appropriate SLURM file (with the correct export OMP_NUM_THREADS line) as part pipeline workflow and, if so, merge this change into master.

[coveralls]

Coverage decreased (-0.0008%) to 26.591% when pulling fe05a36 on openmp-slurm into ee26999 on master.

[sbailey]

Looks good, thanks. While testing this I also fixed a pre-existing help string bug in desi_run_night --dry-run-level (which I thought we had previously fixed but maybe in a PR that was abandoned).

This PR works as expected/advertised for desi_proc and desi_run_night for arc, flat, and science exposures. Let's wait to Monday to merge to not have too many moving parts over the weekend, even if it seems obvious that this should be ok.