Add support for specialized threads

* Add "--thread-spec" option to salloc, sbatch and srun commands. This is
  the count of threads reserved for system use per node.
* Add ability for scontrol to get/set job ThreadSpec
* sivew: Add job ThreadSpec field to get/set
* Modify select/cons_res to manage job allocations while leaving specialized
  threads for system use.
* core_spec plugins: Fix system task binding logic and logging
* Modify squeue output for thread_spec values
* task/affinity and cgroup: Enhanced task binding logic