Get rid of all exec calls and work only in the PHP space when launching jobs.

run_local and run_mosix are now obsolete.

Also, use only phpseclib for the SSH connections (no more OS level).
Login via phpseclib rather than sshpass.
Introduce the CLUSTER_SCHEDULER configuration variable to configure the cluster scheduler.

Example usage:
// we replace {MEMORY} with a memory requirement
// and {COMMAND} with the command to schedule
define('CLUSTER_SCHEDULER', 'nohup /bin/mosbatch -q -b -m{MEMORY} {COMMAND}');
Get rid of run_* files.