[server] refactor cleanup() code used by "cubicweb-ctl delete" Try to make each logical step (i.e. "delete database" and "delete user") a bit more visible and explicit. This is a preparatory work to easily plug the "delete namespace" feature.

<div id="ajaxroot">
  <div class="ajaxHtmlHead">
    <script src="http://foo.js" type="text/javascript"> </script>
    <link rel="stylesheet" type="text/css" media="all" href="qunit.css" />
  </div>
  <h1>Hello</h1>
</div>