title: Error on res.users.form when update a custom module
body: <p>I have created a new custom module for Odoo 8 and I have created a new group for secure this module. The security.xml is like this:</p>
  
  <pre class="lang-xml prettyprint-override"><code>    &lt;record model="ir.module.category" id="testmodule_category_testmodule"&gt;
          &lt;field name="name"&gt;Test&lt;/field&gt;
          &lt;field name="sequence"&gt;20&lt;/field&gt;
      &lt;/record&gt;
  
      &lt;record id="testmodule_group_manager" model="res.groups"&gt;
          &lt;field name="name"&gt;Manager&lt;/field&gt;
          &lt;field name="category_id" ref="testmodule_category_testmodule"/&gt;
      &lt;/record&gt;
  </code></pre>
  
  <p>When I install this custom module for the first time it works everything ok but if I update this module, when I try to access to <em>Configuration->Users->Users</em> I get this error:</p>
  
  <pre><code>File "D:\work\odoo\odoo\openerp\addons\base\ir\ir_ui_view.py", line 369, in raise_view_error
  raise AttributeError(message)
  AttributeError: El campo `in_group_15` no existe
  
  Error de contexto:
  Vista `res.users.form`
  [view_id: 153, xml_id: base.view_users_form, model: res.users, parent_id: n/a]
  </code></pre>
  
  <p>Also, I have created a new module from <i>odoo.py scaffold</i> and only added this security.xml for testing this error, but I get always this when update the module. If I remove and reinstall it works fine but not when update.</p>
  
  <p><strong>UPDATE</strong></p>
  
  <p>If I get a fresh install of Odoo it works fine, install, uninstall and upgrade module. Maybe there are a conflict with another module. In the fields list I don't see any module field named 'in_group_15'. How can I get what module is the conflict?</p>