Make the notes docker image use devstack settings by default

This is the status quo for all other IDAs, and also this is required for
our current devstack tooling which just assumes the default settings are
for devstack.

docker/build/notes/ansible_overrides.yml

@@ -4,3 +4,8 @@ EDX_NOTES_API_MYSQL_HOST: 'db'
 EDX_NOTES_API_ELASTICSEARCH_URL: 'http://es:9200/'
 COMMON_MYSQL_MIGRATE_USER: '{{ EDX_NOTES_API_MYSQL_DB_USER }}'
 COMMON_MYSQL_MIGRATE_PASS: '{{ EDX_NOTES_API_MYSQL_DB_PASSWORD }}'
+
+# For the docker image, force it to use the devstack settings instead of the
+# default production settings (notesserver.settings.yaml_config).
+# This is also consistent with all other IDAs.
+EDX_NOTES_API_DJANGO_SETTINGS_MODULE: 'notesserver.settings.devstack'