Improve selection of jobs to preempt when there are multiple partitions
    with jobs subject to preemption.
bug 3824

Prevent segfault from pointer dereference to the QOS that is
being deleted.

Fix to commit 3e8aa451.

Fix regression from commit c05dcb8a (bug 1923) that doesn't take
into consideration a blank char * as a valid option.

This fixes the scenario like

sacctmgr list associations user=''

which would only print account associations.
Bug 3862

a good return code.

This also fixes the situation where the step was ending but not yet ended
so it sends the KILL_TASK_FAILED error instead of JOB_NOTRUNNING.

Also it removes the abort in favor of exit which it should had been anyways.

Bug 3758

list_for_each)

Inadvertently set to one when requested.

Bug 3855.

Bug 3857.

purge_files_list.

File deletion can be slow, especially when StateSaveLocation in on
NFS or other network filesystems. Since purge_old_job() holds all
the slurmctld write locks, this is especially performance sensitive.

Moving this to an independent thread lets the slower filesystem
cleanup happen without owning these locks. purge_old_job() then
results in the purged job ids being queued in the purge_list.

A race with the job id potentially wrapping around again is already
prevented by _dup_job_file_test() in get_next_job_id().

Bug 3763.

Only called from _list_delete_job once the MinJobAge has
passed.

This will need to be handled differently. The timeout can
lead to the purge process falling further and further behind
on high throughput systems if the number of job scripts that
can be deleted within a second is lower than the job submission
and completion rate of the cluster, eventually leading to
the MaxJobCount limit being reached.

Bug 3763.

it works better on multi-slurmd installs.

Revert some of my b50f4661. Elaborate on tradeoffs, and point
to HTC page as well which is a better location for this info.

This is better discussed in the high_throughput.shtml doc.

Also, "Contrain" is misspelled adding to the confusion.

Bug 3840.

node_featurs/knl_cray plugin: Don't clear configured GRES from non-KNL node.
bug 3768

Initial fix for handling floating partitions that use qos grp limits.

Bug 3776

the SchedulerParameters=reduce_completing_frag option.

NOTE: reduce_completing_frag on or off only works with CompletingWait set to
something.

Bug 3756

This will improve performance and simplify the code.
bug 3757

bug 3754

For jobs submited to multiple partitions, report the job's earliest start
    time for any partition.
bug 3754

Burst buffer jobs cannot be run as root currently, change
test to prevent that.

Bug 3723.

Bug 3756

Bug 3756