[product: zaphod][project: zaphod-v0.3]: Get IP address given a MAC address.

SYNOPSIS
[modified]m42/iputil.py: Implemented mac2ip, arp_table and print_arp_table.
[modified]m42/test/test_iputil.py: Unit test mac2ip, arp_table.

DETAILS
Implemented mac2ip that gets the IP address corresponding to a given
MAC address. This is used by Zaphod to infer the IP address of a
VM using bridged networking.