Fix bug in slurmctld parsing of config file that can cause seg fault.

"Scontrol abort" works. It was leaving a hung pthread due to a recent
   change.
Fix a couple of potential memory leaks
"switch_type" has been added to config data structure, un/pack, etc,
   but not yet reported to the user or documented yet.
The plugins now use function calls to get a their type and plugin directory
   from a common data structure rather than individually reading and
   parsing the configuration file.