plugin on stepd launch.

Not only that, but also make it so the slurmd sends this information over to
the stepd on init.

This also makes it so GRES of the same name and different types can happen.

Hopefully no functionality change.

by similar combining code from all the gres plugins.  Hopefully improving
maintenance.

into gres_plugin_state_file.  Hopefully no functionality change.

of 2 exactly same code paths, hopefully no functionality change.

Regular user use of "scontrol top" command is now diabled. Use the
   configuration parameter "SchedulerParameters=enable_user_top" to enable
   that functionality. The configuration parameter
   "SchedulerParameters=disable_user_top" will be silently ignored.
bug 3653

Bug 4220.

to account for changes made in 8014b5a4

Can set limits based off of TRESBillingWeights value.

Bug 4162.

Coverity CID 144120

Coverity CID 44803

Coverity CID 44813

Fix of 0ce35824

Before:
$ sbatch --wrap="sleep 300"
Submitted batch job 228
$ squeue
             JOBID PARTITION     NAME     USER ST       TIME   CPUS NODELIST(REASON)
               228     debug     wrap    brian PD       0:00      1 (AssocMaxUnknownPerNode)

Fixed:
$ squeue
             JOBID PARTITION     NAME     USER ST       TIME   CPUS NODELIST(REASON)
               229     debug     wrap    brian PD       0:00      1 (AssocMaxCpuPerNode)

$ sacctmgr mod account stuff set maxtrespernode=cpu=-1,mem=1
$ squeue
             JOBID PARTITION     NAME     USER ST       TIME   CPUS NODELIST(REASON)
               229     debug     wrap    brian PD       0:00      1 (AssocMaxMemPerNode)

$ sbatch --wrap="sleep 300" --gres=blah:2 -pgpu
Submitted batch job 235
$ squeue
             JOBID PARTITION     NAME     USER ST       TIME   CPUS NODELIST(REASON)
               235       gpu     wrap    brian PD       0:00      1 (AssocMaxGRESPerNode)

Coverity CID 177813

bug 3673

Bug 4200.

Make this a fatal(), rather than delaying until a symbol error is thrown
when attempting to load the plugin. Update some docs as well.

Bug 4123.

This has been documented this way for a long time, but not strictly
enforced. Enforce it now. (Of course, the real enforcement is still
present within slurmctld. But this denies you up front with a more
obvious error.)

Bug 4101.

Bug 4199.