Incorrect error codes returned in some cases, especially if the slurmdbd is down

Previously for linux systems all information was placed on a single line.

was setting task count to ntasks-per-node times min node count.
Now leaves ntasks unset

interface instead of through the normal method.

In order to avoid the removal/creation of the slurm root cgroups
of the managed subsystems, disable the notify_on_release to prevent
the release agent from removing them automatically.

In order to be more deterministic in the removal of the different layers
of memcg involved when a step is running, do it manually by first acquiring
a lock on the root memcg to protect concurrent creations of step memcg from
invalid intermediate memcg directories in their own hierarchies.

Now relies on the task_pre_launch_priv to add tasks to the
step memcg and delete it at the end of the step.
slurmstepd no longer has to be added to any memcg for the
logic to work.

Prepare the use of task_pre_launch_priv to attach tasks to
the various cgroup subsystem in order to no longer have to
add the slurmstepd to the cgroup and let him belong to the
default cg of each subsystem.

This privileged call is executed just after the fork of each
forked task by user root before becoming the user. It enables
the task plugin to perform actions as a privileged user in
every task context.