Fixes #5846: Use portable init handling in system Techniques

Ticket: http://www.rudder-project.org/redmine/issues/5846

To be merged in 3.0
cron is restarted automatically by init on AIX:
```
bash-4.2# cat /etc/inittab |grep cron
cron:23456789:respawn:/usr/sbin/cron
```

No need to do it ourselves :)