If the VirtualBox guest property /VirtualBox/GuestInfo/Net/1/V4/IP
returns an IP address ending in .1, raise an error.
This addresses an issue that was revealed as an NFS error, where Vagrant
was creating an exports file with the wrong IP address. This was thought
to be caused by the presence of a docker0 interface, but it manifested
itself even without Docker installed.
This issue is difficult to reproduce, but hopefully this PR will get us
closer to the root cause.
f593bb54d2