[PATCH 3/5] Add Layouts= conf pragma support in slurm.conf for layouts management

This new pragma will be used to define the list of layouts to load at startup.
It will consist of comma separated values of layouts type and optional names,
respecting the following pattern : Layouts=layout_type[/layout_name][,...]
In case the name would not be defined, "default" would be assumed.

(Adapted for slurm-14.11 by Matthieu Hautreux <matthieu.hautreux@cea.fr>)