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 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.

Bug 3921.

Bug 4062.

Bug 4084

bug 3824

Do not run the Node Health Check on termination of the external
  step as this happens when the job allocation ends and the job
  NHC will be executed anyway.
Bug 4074

instead of waiting till end of script.

Bug 1286