Fix Vagrant issue when also running govuk dev VM

"[pp-development-1] Clearing any previously set network interfaces...
The specified host network collides with a non-hostonly network!
This will cause your specified IP to be inaccessible. Please change
the IP or name of your host only network to not match that of
a bridged or non-hostonly network."
Merge pull request #3 from alphagov/tweaks

Fix Vagrant issue when also running govuk dev VM