Update horizon wsgi wrapper to the recommended one

During Rocky cycle, horizon updates the path of the wsgi wrapper
to the one recommended by Django [1]. The old path will be dropped
in the T release.

[1] https://review.openstack.org/#/c/561802/

Related-Bug: #1763204
Change-Id: Ie942518b587d193a7de55ffcc0a2848406146eb2

Author: amotoki

files/apache-horizon.template

@@ -1,5 +1,5 @@
 <VirtualHost *:80>
-    WSGIScriptAlias %WEBROOT% %HORIZON_DIR%/openstack_dashboard/wsgi/django.wsgi
+    WSGIScriptAlias %WEBROOT% %HORIZON_DIR%/openstack_dashboard/wsgi.py
     WSGIDaemonProcess horizon user=%USER% group=%GROUP% processes=3 threads=10 home=%HORIZON_DIR% display-name=%{GROUP}
     WSGIApplicationGroup %{GLOBAL}