SSH processes do not die

SSH processes stay in the main node

```
root      973703       1  0 Mar21 ?        00:01:11 ssh -o
ServerAliveInterval=1 -o ControlPersist=no -2MNax -o BatchMode=yes -S
 /root/.libnet-openssh-perl/05ad0cfff02d21666788b0ca02bc7932 
```

Reported by @gmiranda 