title: Symfony 3 validation groups inside child entity ignored
body: <p>I have a simple form, with two fields, email and name. email is in Accounts entity and name in child entity: MedicalCenters</p>
  
  <pre><code>use Symfony\Component\Form\AbstractType;
  use Symfony\Component\Form\Extension\Core\Type\TextType;
  use Symfony\Component\Form\FormBuilderInterface;
  use Symfony\Component\OptionsResolver\OptionsResolver;
  use Symfony\Component\Validator\Constraints\Email;
  use Symfony\Component\Validator\Constraints\NotBlank;
  
  class AccountsMedicalCentersType extends AbstractType
  {
      public function buildForm(FormBuilderInterface $builder, array $options)
      {
          $builder
              -&gt;add('email')
              -&gt;add('name', TextType::class, array(
                  'mapped' =&gt; false
              ));
      }
  
      public function configureOptions(OptionsResolver $resolver)
      {
          $resolver-&gt;setDefaults(
              array(
                  'validation_groups' =&gt; array('emailValidation','Default')
                  )
          );
      }
  }
  </code></pre>
  
  <p>I would like to validate the fields with validation groups because in the MedicalCenters entity I have some other validation, for other situations:</p>
  
  <p>Accounts Entity, validation works fine:</p>
  
  <pre><code>/**
       * @var string
       *
       * @ORM\Column(name="email", type="string", length=100, nullable=true, unique=true)
       * @Assert\NotBlank(groups={"emailValidation"})
       * @Assert\Email(groups={"emailValidation"})
       *
       */
      protected $email;
   /**
       * @var \MedicalCenters
       *
       * @ORM\ManyToOne(targetEntity="MedicalCenters")
       * @ORM\JoinColumns({
       *   @ORM\JoinColumn(name="medical_centers_id", referencedColumnName="id")
       * })
       *
       * @Assert\Valid
       *
       */
      private $medicalCenters;
  </code></pre>
  
  <p>MedicalCenters Entity, the validation groups are ignored and the error returned is the second one (address not blank):</p>
  
  <pre><code>/**
       * @var string
       *
       * @ORM\Column(name="name", type="string", length=300, nullable=true)
       * @Assert\NotBlank(message="name not blank", groups={"emailValidation"})
       *
       */
      private $name;
  
      /**
       * @var string
       *
       * @ORM\Column(name="address", type="text", length=65535, nullable=true)
       * @Assert\NotBlank(message="address not blank")
       */
      private $address;
  </code></pre>
  
  <p>I don't understand why from the child entity is not validate only the name field, which belong to the group emailValidation? 
  What am I doing wrong?</p>
  
  <p>In the controller I have:</p>
  
  <pre><code>$form = $this-&gt;createForm(
                  AccountsMedicalCentersType::class,
                  $currentAccount,
                  array(
                      'validation_groups' =&gt; array(
                          'emailValidation',
                          'Default'
                      )
                  )
              );
  </code></pre>
  
  <p>Thanks</p>