Add DJFS settings (OSPR-50)

Add DJFS settings (OSPR-50)
To solve this pr:
https://github.com/edx/edx-platform/pull/5291

playbooks/roles/edxapp/defaults/main.yml

@@ -18,6 +18,8 @@
 # Bucket used for xblock file storage
 EDXAPP_XBLOCK_FS_STORAGE_BUCKET: "None"
 EDXAPP_XBLOCK_FS_STORAGE_PREFIX: "None"
+EDXAPP_DJFS: "None"
+
 EDXAPP_LMS_BASE: ""
 EDXAPP_PREVIEW_LMS_BASE: ""
 EDXAPP_CMS_BASE: ""
@@ -515,6 +517,7 @@ edxapp_generic_auth_config:  &edxapp_generic_auth
   GOOGLE_ANALYTICS_ACCOUNT: "{{ EDXAPP_GOOGLE_ANALYTICS_ACCOUNT }}"
   THIRD_PARTY_AUTH: "{{ EDXAPP_THIRD_PARTY_AUTH }}"
   AWS_STORAGE_BUCKET_NAME: "{{ EDXAPP_AWS_STORAGE_BUCKET_NAME }}"
+  DJFS: $EDXAPP_DJFS
 
 generic_cache_config: &default_generic_cache
   BACKEND:  'django.core.cache.backends.memcached.MemcachedCache'