Support change of DebugFlag=Switch on reconfig or manual reset

src/common/switch.c

src/common/switch.h

src/plugins/switch/none/switch_none.c

src/plugins/switch/nrt/switch_nrt.c

src/slurmctld/proc_req.c

src/slurmctld/read_config.c

src/slurmd/slurmd/slurmd.c