Use a xenial base box: I don't know the url, do I need to?

vagrant/base/devstack/Vagrantfile

@@ -15,9 +15,9 @@ end
 
 Vagrant.configure(VAGRANTFILE_API_VERSION) do |config|
 
-  # Creates a devstack from a base Ubuntu 12.04 image for virtualbox
-  config.vm.box     = "precise64"
-  config.vm.box_url = "http://files.vagrantup.com/precise64.box"
+  # Creates a devstack from a base Ubuntu 16.04 image for virtualbox
+  config.vm.box     = "ubuntu/xenial64"
+  #config.vm.box_url = "http://files.vagrantup.com/ubuntu/xenial64.box"
 
   config.vm.network :private_network, ip: vm_guest_ip