Enhance iptables setup

Enhance iptables setup so it is stateless by using the recent module
to autoblock users violating iptable rules. This rate limiting is in
effect for ICMP (ping), NTP, and SSH. If the machines are on the same
local subnet then rate limiting is bypassed. SSH rate limiting can be
configured per server type. Other public IPs can be configured to
bypass rate limiting as needed.

Change-Id: Ia3c3b10bae71fe8a6a62b13a6ebbb9ad21e49006
Implements: blueprint infra-iptables