Native persistence

Having another stab at this. Working with some caveats. Unsure how to test the util method. Soliciting comments..

--

Call the necessary commands from the provider to persist rules between
reboots. Tested on the following distros:

- CentOS 5.8
- CentOS 6.3
- Ubuntu 10.04
- Ubuntu 12.04
- Debian 6

Cavaets:

- Persistence may fail on the first run if Firewall resources are actioned
  before the Package resource.
- Older iptables-persistent doesn't support the restoration of ip6tables.
- ebtables cannot be restored.