Fix minor regression about old apps not getting per_form_csrf and request_forgery_protection configs

- Earlier per_form_csrf_tokens and request_forgery_protection config
  files were generated for old apps upgraded to Rails 5.
- But when we collapsed all initializers into one file, the entire file
  does not get created for old apps.
- This commit fixes it and also changes values for all new defaults for
  old apps so that they will not break.
- Also added a test for `rails app:update`.