Install Django then Avocado to respect travis Django version

Previously, Avocado was installed first and one of its dependencies was Django. During the dependency installation for Avocado, it was always installing Django 1.5.1 meaning we were only testing 2 of the planned 4 configs, that is Python 2.6 and 2.7 under Django 1.5.1 completely missing the Django 1.4.5 configs.