Minor updates to MCS logic

Added #define JOB_SHARED_* varilables to slurm.h
Replaces some blocks of spaces with tabs
Remove test of MCS_Plugin from client where job is submitted as
  a means of determining if an --mcs-label option is supported.
  This will not work for jobs being submitted between systems,
  which will become common in slurm v16.05. The check will need
  to be performed in the (slurmctld) server.