Fix provisioning with Ubuntu host + Ubuntu guest

See hashicorp/vagrant#516. It’s not actually a Vagrant problem, but a
seemingly long-unfixed Virtualbox one, still in new releases.

Vagrantfile

@@ -36,6 +36,7 @@ Vagrant.configure("2") do |config|
   config.vm.provider "virtualbox" do |v|
     v.memory = 2048
     v.cpus = 2
+    v.customize ["modifyvm", :id, "--nictype1", "Am79C973"]
   end
 
   config.vm.provision "ansible" do |ansible|