This commit takes a big step towards ensuring that iptables rules are
always kept in the correct order. Specifically, when re-setting a a
ruleset, any time a rule is missing, that rule and all following rules
are re-added to ensure that from that index onwards all rules are in the
right order. Similarly, when reconciling an existing ruleset against the
backend, if a rule is missing, that rule an all following rules are
re-added.
This change does not guarantee that the order of rules in the backend
is correct. Unless an actor is modifying the order of rules in iptables,
all rules created by Kilo should now be kept in the correct order.
Fixes: #19
