FIX: controller terminates when calling SleeperModule stop() - stop() should not run terminate() when called by controller
Reintroduced _get_command_available  (apparently it was being used...)
Added _last_pid for storing the pid of the last process to run the instance even after process death so we can handle process termination from controler.
SIGCHLD handling to be aware of child / instance termination. Not doing anything yet when instances crash.