Db prefix should be used for the subjects DB too (#13)

* DB_WHISK_AUTHS=local_subjects instead of `subjects`
diff --git a/docker-compose/docker-whisk-controller.env b/docker-compose/docker-whisk-controller.env
index b690b28..e9f9c4b 100644
--- a/docker-compose/docker-whisk-controller.env
+++ b/docker-compose/docker-whisk-controller.env
@@ -11,7 +11,7 @@
 
 DB_PREFIX=local_
 DB_WHISK_ACTIONS=local_whisks
-DB_WHISK_AUTHS=subjects
+DB_WHISK_AUTHS=local_subjects
 
 KAFKA_NUMPARTITIONS=1