fix/BROOKLYN-36

fix saveIptablesRules
`iptables-persistent` saves the current ipv4 and ipv6 firewall rules during the installation.
So `saveIptablesRules` need to invoke `sudo /etc/init.d/iptables-persistent save` as explained [here](http://askubuntu.com/questions/119393/how-to-save-rules-of-the-iptables) to save rules using `iptables-persistent`

Notice also that as we enable `DEBIAN_FRONTEND=noninteractive` for apt-get install, the problem described [here](http://askubuntu.com/questions/339790/how-can-i-prevent-apt-get-aptitude-from-showing-dialogs-during-installation) is solved. 

I've tested the command on an empirical test on a centOS 6 server and a Debian 7 server