onramp_iptables: Fix a typo and logging

Make logs separate for each run for better debugging, and fix a typo in the create_mapping call

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
onramp: Add interface and external_addrs options

Adding options to support specification of external interface and external ip
addresses to manager.  This probably isn't the best way to do address
specification, but it will do for PoC and likely change later

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>