Rename config references

Author: gururajsh

app/models/runtime/stack.rb

@@ -1,5 +1,5 @@
 require 'models/helpers/process_types'
-require 'models/helpers/config_file'
+require 'models/helpers/stack_config_file'
 
 module VCAP::CloudController
   class Stack < Sequel::Model

lib/tasks/stack_check.rake

@@ -7,7 +7,7 @@ namespace :stacks do
     next unless db.table_exists?(:buildpack_lifecycle_data)
 
     RakeConfig.config.load_db_encryption_key
-    require 'models/helpers/config_file'
+    require 'models/helpers/stack_config_file'
     require 'cloud_controller/check_stacks'
     VCAP::CloudController::CheckStacks.new(RakeConfig.config, db).validate_stacks
   end