Log proper backfill job test time

The backfill scheduler was always reporting the time that a job
was being considered as NOW rather than the time that was really
being considered.
sched/backfill performance improvements

Remove duplicate backfill scheduling tests. For example there is
no need to test if a job can be started if the only difference
from the previous test involves nodes in other partitions that
can not be used by the job we are trying to start.