delete vagrant vm's chef client and node from chef server on destroy

middleware.rb

class OnDestroyMiddleware
  def initialize(app, env)
    @app = app
  end
  
  def call(env)
    `knife client show #{env["config"].chef.node_name}`
    if $?.to_i == 0
      env.ui.info "Removing client #{env["config"].chef.node_name}"
      `knife client delete #{env["config"].chef.node_name} -y`
    end
    `knife node show #{env["config"].chef.node_name}`
    if $?.to_i == 0
      env.ui.info "Removing node #{env["config"].chef.node_name}"
      `knife node delete #{env["config"].chef.node_name} -y`
    end
    @app.call(env)
  end
end