Create integration tests

Integration tests for adventure.

Note that SeleniumBaseTest should be put into xblock-utils later.
Two little things here:
1. It's confusing to have `xml_path` as an argument to this method, since `xml_path` is already defined in the outer function on line 21. Since you are referring to `relative_scenario_path` from the outer context as part of this method, you should just get `xml_path` from the outer context as well.
2. The local `scenarios` variable here is masking `from workbench import scenarios` - would make the code clearer if you rename it.