It rewrites some parts of the conf regen but try to keep as much as possible
the same logic - to prevent a too big refactoring. The main change is that
configuration file regen is now handle by service_regen_conf directly.
Hooks are now called twice with the following arguments respectively:
* `"pre" $force $pending_dir`: it's time for the script to generate and put
each configuration file to update/remove into `$pending_dir` with the
right directory tree. To remove one, just touch an empty file.
* `"post" $force`: this second time, the script may restart services, fix
permissions, clean, ...
Between this two executions, the service_regen_conf will look for any files
under the `$pending_dir` and safely process them - either create, update or
remove the proper system configuration.
