fix bug in gres state save/restore for a node

Better handling of select plugins that don't exist on various systems for cross cluster communication.  Slurmctld, slurmd, and slurmstepd now only load the default select plugin as well.

various gres tweaks, modify help message, add cpu count to gres registration msg, validate cpu list in gres.conf

Added preempt_mode option to qos.  Also added quite a bit of logic to add options for for new cpu_run_mins limits