tests: Also mock `open` in Jinja to be able to use templates in bake tests. This also required raising the proper exception in the mock function. We are now raising `IOError` and set the `errno` attribute on it.

{
  "name": "PieCrust",
  "version": "0.0.1",
  "private": "true",
  "dependencies": {
    "bootstrap": "~3.3.2"
  }
}