prevent generation of random SSH keys done in hashicorp/vagrant#2608

Vagrantfile

@@ -4,6 +4,7 @@ Vagrant.configure(2) do |config|
       c.vm.box = "ubuntu/trusty64"
       c.vm.hostname = "ansible-#{i}"
       c.vm.network "public_network"
+      c.ssh.insert_key = false
     end
   end
 end