advanced slurm support --cpus-per-task

[jennfshr]

add --cpus-per-task as a {{sched.test_cmd}} option at parallel launch

       -c, --cpus-per-task=<ncpus>
              Advise the Slurm controller that ensuing job steps will require ncpus number of  processors
              per  task.  Without this option, the controller will just try to allocate one processor per
              task.

              For instance, consider an application that has 4 tasks, each requiring  3  processors.   If
              our  cluster is comprised of quad-processors nodes and we simply ask for 12 processors, the
              controller might give us only 3 nodes.  However, by using  the  --cpus-per-task=3  options,
              the  controller  knows  that each task requires 3 processors on the same node, and the con-
              troller will grant an allocation of 4 nodes, one for each of the 4 tasks.