title: Validation rules not working when embedding FOSRegistrationFormType
body: <p>Hi I want to embed part of registration form from FOSUserBundle into another one. When I tried to add existing email, "Integrity constraint violation" exception was raised because unique validator is not used. How can I fix this. When registration form is used separately, validators are working correctly.</p>
  
  <p>Main form:</p>
  
  <pre><code>class SoldierType extends AbstractType
  {
      public function buildForm(FormBuilderInterface $builder, array $options)
      {
          $builder
              ...
              -&gt;add('user', new NameFormType('Application\Sonata\UserBundle\Entity\User')) 
  
          ;
  
      }
  
      public function setDefaultOptions(OptionsResolverInterface $resolver)
      {
          $resolver-&gt;setDefaults(array(
              'validation_groups' =&gt; array('registration')
          ));
  
      }
  
      public function getName()
      {
          return 'wnc_soldierbundle_soldiertype';
      }
  }
  </code></pre>
  
  <p>NameForm</p>
  
  <pre><code>namespace Application\Sonata\UserBundle\Form\Type;
  
  use Symfony\Component\Form\AbstractType;
  use Symfony\Component\Form\FormBuilderInterface;
  use Symfony\Component\OptionsResolver\OptionsResolverInterface;
  use FOS\UserBundle\Form\Type\RegistrationFormType as BaseForm;
  
  class NameFormType extends BaseForm
  {
  
      public function buildForm(FormBuilderInterface $builder, array $options)
      {
          $builder-&gt;add('firstname')
                  -&gt;add('lastname')
                  -&gt;add('email', 'email', array('label' =&gt; 'form.email', 'translation_domain' =&gt; 'FOSUserBundle'));
  
      }
  
  
      public function getName()
      {
          return 'fos_user_name';
      }
  
  }
  </code></pre>