Test frameworks path overrides

* Add tests for framework install_path system. Ensuring the configuration takes
  precedence if present, or build sane defaults otherwise.
* Also, ensure that all frameworks tests are called without any local xdg
  configuration file.
* Fix how we load the frameworks (for multiple reloads, like in ours tests)
  and reset the xdg config directories
* Fix as well by explicitely telling we expect an error message, which was
  shadowed by a lack of super() call in setUp()