Add --trace or --nictrace option

[RichWellum]

#29 - added a new debug option, commented out.

# run(['VBoxManage', 'modifyvm', vmname, '--nictrace1', 'on',
#      '--nictracefile1', os.path.join(base_dir, 'Mgmt.pcap')])

future feature may be to add this to a --trace option in this tool.