Permit job with invalid QOS to run if QOS set by administrator

About a year ago I submitted a modification that you incorporated
into SLURM 2.4, which was to allow an admin to modify a job to use
a QOS even though the user did not have access to the QOS.

However, I must have tested it without having the Accounting set
to enforce QOS's. So, if an admin modifies a job to a QOS they
don't have access to, it will be modified, but the job will result
in a state of InvalidQOS, which is reasonable, since this would
handle the case where a user has their QOS removed. A problem,
however, is that even though the scheduler won't schedule the job,
backfill still will.

One approach would be to fix backfill to be consistent with
the scheduler (which should probably occur regardless), but
my thought would be to modify the scheduler to allow the QOS
as long as it was set by an admin, since that was the intent
of the modification to begin with.

I believe it  would only take a single line to change, just
adding a check on the job_ptr->limit_set_qos, to make sure
it was set by an admin:

                if (job_ptr->qos_id) {
                        slurmdb_association_rec_t *assoc_ptr;
                        assoc_ptr = (slurmdb_association_rec_t *)job_ptr->assoc_ptr;
                        if (assoc_ptr &&
                            !bit_test(assoc_ptr->usage->valid_qos,
                                      job_ptr->qos_id) &&
                            !job_ptr->limit_set_qos) {
                                info("sched: JobId=%u has invalid QOS",
                                        job_ptr->job_id);
                                xfree(job_ptr->state_desc);
                                job_ptr->state_reason = FAIL_QOS;
                                continue;
                        } else if (job_ptr->state_reason == FAIL_QOS) {
                                xfree(job_ptr->state_desc);
                                job_ptr->state_reason = WAIT_NO_REASON;
                        }
                }

Phil