Restore use of DNS from Vagrant VMs

These incantations are said to fix DNS on Vagrant VMs running with a
private network.

Vagrantfile

@@ -4,10 +4,15 @@ vm_ip = "172.16.0.3" # arbitrary private IP
 pkgs = "lxc-docker build-essential ethtool libpcap-dev git mercurial bc"
 
 Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
+
   config.vm.box = "phusion/ubuntu-14.04-amd64"
   config.vm.box_url = "https://oss-binaries.phusionpassenger.com/vagrant/boxes/latest/ubuntu-14.04-amd64-vbox.box"
 
   config.vm.network "private_network", ip: vm_ip
+  config.vm.provider :virtualbox do |vb|
+    vb.customize ["modifyvm", :id, "--natdnshostresolver1", "on"]
+    vb.customize ["modifyvm", :id, "--natdnsproxy1", "on"]
+  end
 
   config.vm.synced_folder ".", "/vagrant", disabled: true
   config.vm.synced_folder ".", "/home/vagrant/src/github.com/zettio/weave"

test/Vagrantfile

@@ -33,6 +33,11 @@ end
 
 Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
 
+  config.vm.provider :virtualbox do |vb|
+    vb.customize ["modifyvm", :id, "--natdnshostresolver1", "on"]
+    vb.customize ["modifyvm", :id, "--natdnsproxy1", "on"]
+  end
+
   (1..n_machines).each do |i|
     config.vm.define "host#{i}" do |host|
       ip_suffix = ip_suffix_base + i