clean up oardocker cgroup on oardocker stop

[npf]

[npf]

actually do on any "oardocker stop".

remove any subdir (no assumption on names) in the oardocker directories.

should be idempotent (do not report an error if call with nothing to remove)

[npf]

I wrote a simple bash script that can display and clean cpusets -> top_cpuset.sh (see oar branch master-extensible-jobs).
I could be shipped as a oardocker sub command.
(it currently lacks the cleanup of the cgroup subsystems other then cpuset)

[npf]

only the cpuset cgroup subsystem is cleaned currently.

clean others as well.

(using the same script file for both creation and clean-up would be wise)