resolve test_good_repo_and_course_id() testing issue...

The internal server thread started by Django Test for LiveServerTestCase
only supports the app being tested.  Thus, server-side REST calls to
/repo get 404 errors.

Skip unless TEST_PROVIDER is passed in like this:

TEST_PROVIDER=http://127.0.0.1:8000/ ./manage.py test

Presumably that URL is a valid API endpoint which supports the sample
course definitions.