Create the following manually in VirtualBox > Preferences > Network > Host-only Networks.
If the first host-only adapter fails to take the setting after clicking ok and returning to the dialog, try setting the last part of the IP to .2 instead of .1. This seems to be an issue on Windows hosts: http://bit.ly/1vqrEHC.
vboxnet0
10.20.0.1
255.255.255.0
vboxnet1
172.16.0.1
255.255.255.0
vboxnet2
172.16.1.1
255.255.255.0
Then comment out the following line in launch.sh (36):
./actions/create-interfaces.sh || exit 1