Add better default int support to #whoami? via network_interface gem

This MR picks up where we left off on PR #42

1.) Adds network_interface dependency to gemset specification
2.) Adds #default_ip, #rand_port and #default_int helper methods
3.) Fixes #whoami? bug when no parameters are specified the default interface is not returned when it's not the first in the interface list (common problem for Laptop users testing over wireless)