Use shorter Redis key for dir backend config

rsc:db:username instead of rs_config:dir_backend:username

spec/spec_helper.rb

@@ -39,7 +39,7 @@ if app.settings.respond_to? :redis
   end
 
   def purge_redis
-    redis.keys("rs_*").each do |key|
+    redis.keys("rs*").each do |key|
       redis.del key
     end
   end