Fix false positive error from Coverity

A 17.02 controller,sacctmgr couldn't talk to a "master/17.11" DBD
because the 17.02 client was talking attempting to talk to the DBD with
the 17.02's MIN_PROTOCOL_VERSION -- which was 15.08 and is more than 2
version behind the master. The master's MIN_PROTOCOL_VERSION is 16.05,
so it couldn't unpack the messages.

The controller should always communicate at it's current protocol to the
DBD.

For federations, it's possible that a higher version controller could
talk to a lower version controller. So the cluster needs to talk to the
remote cluster using the remote cluster's protocol version -- which is
given back from the DBD.

If you always return SLURM_SUCCESS, you might as well not return
anything at all.

Now that sched/wiki + sched/wiki2 are gone, almost all
of the sched plugin interface are unused. So remove them.

Three of these were encapsulating a call into the gang scheduler,
handle these directly where needed instead of through the sched plugin.

on origin of the enum.

No functional change.

No functional change.

Enable through SchedulerParameters. Will sort by youngest jobs first,
rather than based on priority. Use alongside 'preempt_strict_order' if
you don't want the plugin to try to further optimize the preemption
list.

Bug 3457.

8eac53beef1d added assertions to prevent null buffers.

For unit testing

by assignment of a value to the out_tres_limit_array (the 3rd
argument to the _validate_tres_usage_limits_for_qos function),
I added function _validate_tres_usage_limits with an added
bool argument to check whether the assignment should be made.
_validate_tres_usage_limits_for_{assoc,qos} just calls/returns
_validate_tres_usage_limits with the new bool argument being set for
expected functionality:

out_tres_limit_set == true  same as _validate_tres_usage_limits_for_qos
out_tres_limit_set == false same as
_validate_tres_usage_limits_for_assoc

I went with the call through approach instead of changing the existing
called function names; not knowing if future developments would warrant
the functions diverging further, and so keeping differing function
names a necessity.

dealing with returns from _validate_tres_usage_limits_for_qos and
_validate_tres_usage_limits_for_assoc an enum

_validate_tres_usage_limits_for_assoc an enum (tres_usage_t)

Collapse begin_job_resv_check and fini_job_resv_check into
job_resv_check, and call directly from controller.c rather than
including in job_time_limit.

Introduced by commit 059275f6 when the timer is trigger.
Releasing the locks means that job_ptr may point to an element that was
deleted by a different thread in the meantime. Restructuring the code
to advance the iterator prevents this - the iterator itself does not have
this issue as the List structure will manage the position during the
sleep().

While here, move the reservation update handling outside of this
loop to simplify operation. This does not need to piggy-back on the
scan of the job_list - switching to using list_for_each should
mitigate some of the performance loss by needing a second full pass.

Bug 3414.

# Conflicts:
#	RELEASE_NOTES

These were mis-calculated previously, and are internal implementation details
that weren't meant to be exposed.

association GrpWall limit.

limits.