Add useful utilities for testing, libvirt + increase image size to 2GB

Changes:
- add libvirt installation script in /root/scripts
- add iptables support to kernel (for libvirt)
- increase image size to 2GB (from 1GB) to have more room for packages
- added apt-get upgrade when building boot image
- added various utilities useful for network testing: tcpdump, tshark, nmap etc.