Improve understanding of VirtualBox configuration

There are a couple of recurring VirtualBox issues that are most likely a matter of VM configuration. These issues include

• Missing "host-only" adapter. VirtualBox recently introduced a new NAT layer, which might provide outgoing access and host-guest access at the same time.
• Loss of network connectivity during roaming. Also connected to the NAT layer. VMs should not directly use host services (e.g. DNS server).
• Time skew inside the virtual machine.
• Mounting of NFS shared folders with vagrant. Some issues due to Linux firewalls. Also not preserved on /vagrant mount point during reboot.
• 3D graphics acceleration.
• Benchmark of different virtual I/O sub systems. Perhaps there is better performance with, e.g., virtio.