Add tests for clone_course

PLAT-142

@cpennington @doctoryes plz review
It will raise an exception. My grief with adding a test for it is that it raises an exception not b/c we decided it's wrong to try to do that cloning but b/c we decided not to implement it yet. I always think of tests as testing functional correctness not current state. I can add the test with that caveat I guess.