Store iptables in file

On some machines iptables-restore command
was stucked on waiting for data from stdin.
This patch is redirecting iptables-save and
iptables-restore to/from file. So the worst
thing which could happen is that netns.py
script will fail.

Change-Id: I014ba67c57d8ceb61a906ed018d92dc686620730
Merge "Store iptables in file"