title: Symfony 3.4.4 + FOSUserBundle + Sonata Admin Bundle - User list filtering by role
body: <p>I need:</p>
  
  <ul>
  <li>If the user logged in Sonata Admin is SUPER_ADMIN, see all users</li>
  <li>If the user logged in Sonata Admin is ADMIN, that <strong>NO</strong> see the SUPER_ADMIN</li>
  </ul>
  
  <p>It is to know how, within UserAdmin.php, modify the query by filtering by ROLE</p>
  
  <p>Thank you</p>