Improvements for fault-tolerance work

src/api/node_info.c

src/slurmctld/job_mgr.c

src/slurmctld/node_mgr.c

src/slurmctld/reservation.c

src/slurmctld/reservation.h

src/slurmctld/slurmctld_plugstack.c

src/slurmctld/slurmctld_plugstack.h