Implement an Ubuntu box in the Vagrantfile for exercising multi-OS scenarios

[tima]

In order to support multi-os examples, the Vagrantfile needs a Ubuntu machine. It used to at one point:

cluster.vm.define "node-4" do |config|
  config.vm.box = "ubuntu/trusty64"
  config.ssh.insert_key = false
  config.vm.provider :virtualbox do |vb, override|
    vb.customize ["modifyvm", :id, "--memory", "256"]
    vb.customize ["modifyvm", :id, "--cpus", "1"]
  end
  config.vm.hostname = "node-4"
  config.vm.network :private_network, ip: "10.42.0.9"
end

In addition this node should be added to the static inventory file in the "web" group.

Dependent on #268 getting merged.

[aoyawale]

would something like this work?

#machine.vm.box = "ubuntu/precise64"

#machine.vm.box = "debian/jessie64"

#machine.vm.box = "debian/wheezy64

then you just comment out the one you need.