Modify test for change in sbcast credential validation

User root or SlurmUser don't need valid sbcast credential
Merge branch 'slurm-2.5' of https://github.com/SchedMD/slurm into slurm-2.5
Revision of gres topology bug fix
Add more notes discouraging use of PGSQL plugin
Fix bug in accounting_storage/pgsql
Add debugging hint to MPI guide for MPICH2
Merge branch 'slurm-2.5'