title: "No installed app with label 'admin'" running Django migration. The app is installed correctly
body: <p>I am trying to use <code>admin.LogEntry</code> objects during a datamigration on Django 1.7</p>
  <p>The <code>'django.contrib.admin'</code> app is listed on <code>INSTALLED_APPS</code>.</p>
  <p>On the shell, it works:</p>
  <pre><code>&gt;&gt;&gt; from django.apps import apps
  &gt;&gt;&gt; apps.get_model('admin', 'LogEntry')
  django.contrib.admin.models.LogEntry
  </code></pre>
  <p>But during the migration, it fails:</p>
  <pre><code>def do_it(apps, schema_editor):
      LogEntry = apps.get_model('admin', 'LogEntry')
  </code></pre>
  <p>Fails like this:</p>
  <pre><code>django-admin migrate
  (...)
  LookupError: No installed app with label 'admin'.
  </code></pre>
  <p>Using a debugger, I got that the 'admin' is not installed:</p>
  <pre><code>ipdb&gt; apps.get_apps()
  []
  ipdb&gt; apps.all_models.keys()
  ['website', 'google', 'allauth', 'twitter', 'busca', 'conteudo', 'django_mobile', 'django_filters', 'videocenter', 'tinymce', 'oferta', 'programacaotv', 'contenttypes', 'suit', 'haystack', 'destaque', 'filer', 'galeria', 'auth', 'facebook', 'paintstore', 'critica', 'disqus', 'fichas', 'omeletop', 'autocomplete_light', 'modelsv1', 'temas', 'django_extensions', 'adv_cache_tag', 'taggit', 'social', 'personalidade']
  </code></pre>
  <p>WHY??</p>