Give Resque route a name and use that for the iframe src

Closes #1350

app/views/admin/resque/show.html.haml

 %h3 Resque
-%iframe{src: "/info/resque", width: 1168, height: 600, style: "border: none"}
\ No newline at end of file
+%iframe{src: resque_url, width: 1168, height: 600, style: "border: none"}

config/routes.rb

@@ -10,7 +10,7 @@ Gitlab::Application.routes.draw do
 
   # Optionally, enable Resque here
   require 'resque/server'
-  mount Resque::Server.new, at: '/info/resque'
+  mount Resque::Server.new, at: '/info/resque', as: 'resque'
 
   # Enable Grack support
   mount Grack::Bundle.new({