Redirect to streaming_api_base_url (#3579)

* Redirect to streaming_api_base_url

When Rails receives a request to streaming API, it most likely
means that there is another host which is configured to respond
to it. This is to redirect clients to that host if
`STREAMING_API_BASE_URL` is set as another host.

* Use the new Ruby 1.9 hash syntax

config/routes.rb

@@ -141,6 +141,7 @@ Rails.application.routes.draw do
         resource :public, only: :show, controller: :public
         resources :tag, only: :show
       end
+      resources :streaming,  only: [:index]
 
       get '/search', to: 'search#index', as: :search