If the job step created for external processes (with "PrologFlags=contain")
lacks any accumulated resource use, then don't notify the slurmctld
of completion. This change eliminates an RPC which has no meaningful
data.

Change some job step ID references:
from NO_VAL to SLURM_BATCH_SCRIPT and
from INFINITE to SLURM_EXTERN_CONT

No real change to logic

preempt/job_prio plugin: Implement the concept of Warm-up Time here. Use
the QoS GraceTime as the amount of time to wait before preempting.
Basically, skip preemption if your time is not up.

Conflicts:
	doc/man/man5/slurm.conf.5

Previously was reporting:
Missing node_list for step_id 12727.4294967295

Bug 1548

Conflicts:
	src/common/slurm_protocol_defs.c

Used a value of 3, it should have been a flag, #4

Need to exec() some process since linuxproc will never
signal a process named "slurmstepd"

No changes to logic

This records accounting for the job container created with a
PrologFlags option of "Contain" as added in commit
fc359331

Add PrologFlags option of "Contain" to create a proctrack container at
    job resource allocation time.
At job allocation time, a slurmstepd is spawned on every allocated
    compute node in which to place external processes (e.g. PAM
    can place ssh processes into a cgroup).
This entity is accounted for and reported by sacct as "<jobid>.extern".
Some more testing and development remain, but it mostly works.

Bug 1627