Fix docs translation import errors

When building docs, there are a ton of errors in this format:

AppRegistryNotReady: The translation infrastructure cannot be
initialized before the apps registry is ready. Check that you don't make
non-lazy gettext calls at import time.

Starting in Django 1.7, standalone scripts, such as a sphinx build
require that django.setup() be called first. See:
https://docs.djangoproject.com/en/1.8/releases/1.7/#standalone-scripts

This should be added to the horizon/docs/source/conf.py

Doing so eliminates the errors.

Closes-Bug: #1486139
Change-Id: I0871be3d60d4d78cb430fabdb5725832559191d7

doc/source/conf.py

@@ -24,6 +24,7 @@
 
 from __future__ import print_function
 
+import django
 import os
 import sys
 
@@ -37,6 +38,8 @@ os.environ.setdefault('DJANGO_SETTINGS_MODULE', 'openstack_dashboard.settings')
 
 import horizon.version
 
+django.setup()
+
 
 def write_autodoc_index():