Fix spank_option_getopt in local context

In local context (srun, sbatch, salloc), spank_option_getopt() would
always return that an option was found due to a missing check for
spopt->found in spank_option_getopt.

This patch fixes the issue.
Merge pull request #44 from grondo/slurm-2.5-for-schedmd

Fix spank_option_getopt in local context