Stop rebuilding job's node completing list on reconfig

Removed the call to update_job_nodes_completing() from read_slurm_conf().
Jobs stuck in completing will no longer have all of the nodes of the original
job added to the list of nodes stuck in completing when SIGHUP is sent to the
slurmctld or "scontrol reconfig" is invoked.
Merge pull request #44 from lipari/reconfig_fix

Stop rebuilding job's node completing list on reconfig