Add comments to iptables

Depending on each rule reason we add a relevant comment prefixed
with "snf-network_".

Currently we have three reasons: firewall, proxy-arp, extra.

Additionally save all rules under /etc/iptables/ at the end of
ifup-extra script. This can be used to restore some rules after
reloading ferm.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Fix typo in clear_bridged_setup_firewall

Use $oldchain instead of $chain.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Run snf-network-dnshook only in primary node

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Use hostname -f to get node FQDN

Ganeti exports node names with their FQDN. Use hostname -f
to compare the exported variables and decide whether to execute
the hook or not.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Try clean anything in ifdown

..and don't count on tags, etc. This should work on a best effort
basis.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Fix snf-network-hook

..to delete neighbor proxy only:

1) in old primary node during instance migrate/failover
2) in primary node during instance shutdown/remove

Please note that this is done also by kvm-ifdown-custom.

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Fix typo in delete_neighbor_proxy()

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>
Several syntax fixes in docs

Signed-off-by: Dimitris Aragiorgis <dimara@grnet.gr>