added more info to course metrics

@martynjames  @mattdrayer  added more info to course metrics like `users_started`, `grade_cutoffs`, `num_threads` and `num_active_threads`. 
If the try is protecting us against a specific exception -- in this case CommentClientRequestError -- we should limit the protected logic to only the pertinent code for clarity purposes.  Basically, we should move any/all code that will not throw this exception out of the try block.