Externalize the django settings module as a variable.

playbooks/roles/edxapp/templates/lms.conf.j2

@@ -16,7 +16,7 @@ env WORKERS={{ worker_core_mult.lms }}
 {% endif %}
 env PORT={{edxapp_lms_app_port}}
 env LANG=en_US.UTF-8
-env DJANGO_SETTINGS_MODULE=lms.envs.aws
+env DJANGO_SETTINGS_MODULE={{ edxapp_lms_env }}
 env SERVICE_VARIANT="lms"
 
 chdir {{edx_platform_code_dir}}

playbooks/roles/edxapp/vars/main.yml

@@ -181,9 +181,9 @@ edxapp_lms_preview_app_port: 8020
 
 service_variants_enabled:
   - lms
-  - lms-xml
   - cms
-  - lms-preview
+
+edxapp_lms_env: 'lms.envs.aws'
 
 
 #Number of gunicorn worker processes to spawn, as a multiplier to number of virtual cores