Move cache setup to config/application.rb

Before this change we were trying to configure Rails.cache in an
initializer. It seems that by the time the initializers are loaded,
Rails.cache is already instantiated, so changing the settings does not
achieve anything anymore. This was causing Rails to default to a file
storage cache instead of the Redis cache, which in turn broke `rake
cache:clear`.

config/application.rb

@@ -73,5 +73,24 @@ module Gitlab
         resource '/api/*', headers: :any, methods: [:get, :post, :options, :put, :delete]
       end
     end
+
+    # Use Redis caching across all environments
+    redis_config_file = Rails.root.join('config', 'resque.yml')
+
+    redis_url_string = if File.exists?(redis_config_file)
+                         YAML.load_file(redis_config_file)[Rails.env]
+                       else
+                         "redis://localhost:6379"
+                       end
+
+    # Redis::Store does not handle Unix sockets well, so let's do it for them
+    redis_config_hash = Redis::Store::Factory.extract_host_options_from_uri(redis_url_string)
+    redis_uri = URI.parse(redis_url_string)
+    if redis_uri.scheme == 'unix'
+      redis_config_hash[:path] = redis_uri.path
+    end
+
+    redis_config_hash[:namespace] = 'cache:gitlab'
+    config.cache_store = :redis_store, redis_config_hash
   end
 end

config/initializers/7_cache_settings.rb

-Gitlab::Application.configure do
-  redis_config_file = Rails.root.join('config', 'resque.yml')
-
-  redis_url_string = if File.exists?(redis_config_file)
-                       YAML.load_file(redis_config_file)[Rails.env]
-                     else
-                       "redis://localhost:6379"
-                     end
-
-  # Redis::Store does not handle Unix sockets well, so let's do it for them
-  redis_config_hash = Redis::Store::Factory.extract_host_options_from_uri(redis_url_string)
-  redis_uri = URI.parse(redis_url_string)
-  if redis_uri.scheme == 'unix'
-    redis_config_hash[:path] = redis_uri.path
-  end
-
-  redis_config_hash[:namespace] = 'cache:gitlab'
-
-  config.cache_store = :redis_store, redis_config_hash
-end