title: Capistrano 3: use server custom variable in task
body: <p>I have multi-stage multi-server setup and in my task I need to use server name
  e.g. in stagin.rb I have:</p>
  
  <pre><code>set :stage, :staging
  # Define servers
  server 'xxx.xx.xx.xxx', user: 'deploy', roles: %w{app}, name: 'app1'
  server 'xxx.xx.xx.yyy', user: 'deploy', roles: %w{app}, name: 'app2'
  </code></pre>
  
  <p>and I want to use that "name" variable in my task:</p>
  
  <pre><code>task :configure do
    on roles(:app), in: :parallel do
    # how do I get server name here?
    end
  end
  </code></pre>