title: Rspec Capybara get port before run first visit method
body: <p>I'm try to run Capybara server before all tests to get server port which I should include in url like 'http://subdomain.domain.au:CURRENT_PORT_NUMBER/'
  so</p>
  
  <pre><code># I create new session:
  session = Capybara::Session.new(:selenium)
  # then I start browser
  session.driver.browser
  # And try to get port number like some folks suggested
  Capybara.current_session.driver.rack_server.port # =&gt; nil
  # And get nil
  </code></pre>
  
  <p>In my opinion when browser started you should have port number somewere. Or I'm wrong?
  I do not want hardcode port number for all requests.
  Can anyboady suggest how can I get port to visit my application.</p>
  
  <p>As far as I understand browser it's another process and can be started without local server. Thats make sence only when you query server over network. There should be mechanism to run rack server when 'selenium' test start. Isn't it?</p>