Fix for gres count change

A abort has been reported if the node's gres count differs from
it's bitmap. This has been induced by changing the count manually
(e.g. scontrol update nodename=tux123 gres=gpu:4"). I have not
been able to reproduce this problem, but this will resize the
bitmap in order to avoid the assert failure.
Fix for hwloc returning zero core count
Merge branch 'slurm-2.6'