[COOK-3289] - before_deploy callback should behave like deploy callbacks

* use deploy/before_deploy.rb for before_deploy callback if nothing is
  specified and it exists in the repo

libraries/default.rb

@@ -168,7 +168,7 @@ class Chef
           end
           run_callback_from_file(callback_file)
         when nil
-          nil
+          run_callback_from_file("#{release_path}/deploy/#{what}.rb")
         else
           raise RuntimeError, "You gave me a callback I don't know what to do with: #{callback_code.inspect}"
         end