skip test student and its submissions, etc.

[lsloan]

As asked by @ssciolla in #11 (comment), "Why are we including the test student?"

Test student is included because it has submissions. If the student is not included, errors are caused when trying to save the submissions for a missing user.

Instead, continue inclusion of test student when requesting course users, but don't save it. When the test student is found, make note of its ID. When submissions belonging to the test student's ID is found, skip them.

It's extremely unlikely to happen, but if any peer reviews for the test student's submissions are found, skip those as well.