Enable them onlyh with SchedulerParameters=enable_hetero_jobs OR
  MPI type is "none"

Do pointer comparisons rather than strcmps.
~80x speedup
Bug 3529

e.g.
1000 nodes
8000 tasks
[Sep 11 14:24:15.873639 20992 srvcn        0x7f8c1cdda700] _task_layout_hostfile: hostfile processing took usec=2152678 (orig)
[Sep 11 14:27:46.173424 20992 srvcn        0x7f8c1c6d3700] _task_layout_hostfile: hostfile processing took usec=2142997 (orig)
[Sep 11 14:32:32.245420  4037 srvcn        0x7f12de4e4700] _task_layout_hostfile: hostfile processing took usec=26198 (node ptrs)
[Sep 11 14:36:12.88769   4037 srvcn        0x7f12de6e6700] _task_layout_hostfile: hostfile processing took usec=25515 (node ptrs)
[Sep 11 14:41:38.339162  4037 srvcn        0x7f132c8d5700] _task_layout_hostfile: hostfile processing took usec=27459 (node ptrs)
[Sep 11 15:16:59.575189  1874 srvcn        0x7f3dae3f0700] _task_layout_hostfile: hostfile processing took usec=30129 (node ptrs)
[Sep 11 15:20:50.365004  1874 srvcn        0x7f3dc8b34700] _task_layout_hostfile: hostfile processing took usec=29884 (node ptrs)

Previous logic was recording each character in each node name as
  a separate job component's host name

Commit 241f31d7 resulted in
      heterogeneous jobs not building a valid script unless some
      valid burst buffer plugin was configured (no burst buffer
      plugin resulting in NULL batch script).

After auditing the four calls using this function, it's clear that none
of these fd's are ever meant to leak to a fork()'d process.

Created by VIM if .swp is already in use.

Per the creat() man page, creat() is equivalent to calling open
with flags of O_CREAT|O_WRONLY|O_TRUNC. Add O_CLOEXEC as well.

Only cut over when the heartbeat file is not being updated any longer.

Bug 4142.

Will write out a timestamp into a 'heartbeat' file in StateSaveLocation
every (SlurmctldTimeout / 4) seconds to demonstrate that the primary
controller still has access to the directory, and thus the backup
should avoid taking control.

Bug 4142.

The change from strncpy to strlcpy was chopping off the last character
of the name.

xgroup_set_param() avoids the string parsing overhead and
should be used instead.

Save re-parsing the input string back into the components.

Since ReleaseAgent is no longer required, we can strip out
all the supporting logic for it.

Accidentally removed bracked in checked-in code

If /proc was inaccessible proc_name would leak.

Put an explicit length cap in sprintf to avoid warning. The
size is checked immediate before here so this is just making
the 10-char limit explicit.

Bug 4062.

If the network path to shared storage used for the StateSaveLocation
is separate from that used to communicate with the cluster, both the
primary and backup controllers can end up acting as master on loss
of the cluster network.

Alter the HA takeover code path to make sure that the job state
save file is not still being updated by the primary slurmctld.
If it is, refuse to takeover and retry again later.

Bug 3592.