Prevent a job tested on multiple partitions from being marked

WHOLE_NODE_USER.

If a job is considered on a partition with ExclusiveUser=YES
then it would be marked as if it was submitted with the
--exclusive flag, which would lead to delays launching it
on ExclusiveUser=NO partitions, and cause lower-than-expected
cluster usage.

As a side effect, the job_ptr->part_ptr->flags need to be
tested wherever WHOLE_NODE_USER is considered, instead of
just job_ptr->details->whole_node.

Bug 3771.