include iptables-save into couchbase.log of collectinfo

Change-Id: I8877bb04014d9ddc571547ddb03653e1d27c4164
Reviewed-on: http://review.couchbase.org/43492
Tested-by: Aliaksey Kandratsenka <alkondratenko@gmail.com>
Reviewed-by: Aliaksey Artamonau <aliaksiej.artamonau@gmail.com>