well, basically, when network manager restarts it'll null the values in /etc/resolve.conf this is where we put it for guest customization.
Here are some options:
1.uninstall network-manager with command: #> sudo apt-get purge network-manager network-manager-gnome
2. sudo chattr +i /etc/resolv.conf
This resolution is applicable if you don't want to uninstall the network-manager service
Neither are particularly good, but with transient systems the first option is preferable (forcing it to use the /etc/resolve.conf).