title: Symfony doctrine set database name in migration
body: <p>I want execute migration only for specific database (exist more than 1 database).</p>
  
  <pre><code>public function up()
  {
      $this-&gt;addColumn('user', 'tests', 'string', array('length' =&gt; '255'));
  }
  </code></pre>
  
  <p>I try set: </p>
  
  <pre><code>public function up()
  {
      $this-&gt;addColumn('database.user', 'tests', 'string', array('length' =&gt; '255'));
  }
  </code></pre>
  
  <p>but it not work, symfony try execute this migration for all databases :)</p>
  
  <p>How I can set database name  ?</p>