Changed virtualbox scripts to use Intel 1Gbps NICs
fixed virtualbox scripts to set video memory to 16MB, so it does not complain about non-optimal VM settings in the UI
enabled host i/o cache. it seems to work better with ext4 partitions inside guests
reduced disk sizes in VirtualBox scripts down to 16, 32, and 64GB. previously the largest dist was 2TB, and it was taking 5+ minutes to format it to ext4. this is unacceptable for the end users of VirtualBox scripts