title: How can I display the name of all services with specific tag in symfony2 form
body: <p>I have several services tagged with the same tag. I wonder how to proceed to retrieve the list  of all thoses services and to inject it in a form ?</p>
  
  <p><strong>Here is an exemple of what I want at the end:</strong></p>
  
  <pre><code>$builder-&gt;add('days', 'choice', array(
      'choices' =&gt; $SERVICES,
      'multiple' =&gt; false,
      'expanded' =&gt; false,
      ))
  </code></pre>