Preserve packet:byte counts in iptables_manager.

Preserve packet:byte counts in iptables_manager.

Ported the nova iptables manager code to neutron, so that we
use iptables-save/restore with the -c flag to save/restore
the chains and rules with their packet:byte counts.  All other
changes were ported as well to keep the code as similar as
possible between the two, although they will be different as
I had to fix other bugs found during testing.

Updated tests accordingly to account for new calls and
input/output changes in formatting.

Changed iptables_firewall code to add iptables rules in the same
order that iptables-save will print them: source/dest, protocol,
sport, dport, target; else iptables_manager won't be able
to find them to preserve their [packet:byte] counts.
Tweaked other rules accordingly as necessary.

Fixed a bug introduced in an earlier version of this patch where
_modify_rules() sometimes wouldn't match an existing rule correctly
if not top=true.

Fixes bug 1125393

Change-Id: I858c552d8a7ae24f52f8e8daa05ac37026705773