title: How to capture callback from failed validation in Joi
body: <p>We're building a web service using Hapi. Our routes have some validation. I was wondering if it was possible to capture or override the default callback on failed validation, before or after hapi replies to the client.</p>
  
  <p>my (non-working) code: </p>
  
  <pre><code>{
      method: 'GET',
      config: {
          tags: tags,
          validate: {
              params: {
                  id: Joi.number()
                      .required()
                      .description('id of object you want to get'),
              },
              //Tried this, and it's not working:
              callback: function(err, value) {
                  if (err) {
                      console.log('need to catch errors here!');
                  }
              }
          }
      },
      path: '/model/{id?}',
      handler: function(request, reply) {
          reply('Ok');
      }
  } 
  </code></pre>