Clean up iptables

Implements first part of blueprint infra-iptables.

* Allows machine to talk to itself on its public IP
* Allows ICMP packets (i.e. ping) but  limits it to 1/sec
* Enhance logging

Change-Id: I78271f848e3bb02045ad0249509aaabda7c8c506
Merge "Clean up iptables"