Fix KDC worker process argument parsing

To create worker processes, the KDC shuts down realms, forks off the
worker processes, then reinitializes realms in each child.
Reinitializing realms requires making a second pass over the
command-line arguments.  To do this with getopt, optind must be
reinitialized to 1 for each pass; otherwise, no options will be seen
the second time around.