Change calculation of node's allocated CPUs

Change how a node's allocated CPU count is calculated to avoid double
    counting CPUs allocated to multiple jobs at the same time.
    Previous logic would sum the maximum number of CPUs allocated by each
    partition for any time slice, which could double count CPUs allocated
    to multiple jobs. New logic ORs bitmap of allocated CPUs for every
    partition and time slice, then counts the total for a given node.
    This avoids double counting CPUs allocated to multiple jobs, but
    does not remove from the count CPUs which have been allocated to
    jobs which might be suspended by the gang scheduler (either for
    time slicing or preemption).