Fix for tracking a node's allocated CPUs with gang scheduling.

This bug was introduced by commit 21c52d2f
which fixed a different problem tracking resources associated with suspended
jobs. There are subtle differences between jobs that are suspended by a
user/administrator and jobs suspended by gang scheduling which resulted in
undercounting allocated CPUs when a job suspended by gang scheduling
was active at the same time of a slurmctld reconfiguration request.
See bugs 2353 (original bug related to commit 21c52d2f
and bug 2765