Stop waiting for peers to assess before logging in as a new user

With ~17k submissions pre-loaded in the database, virtual users in the performance test would get stuck waiting for a grade.  These users were last in the queue, so they would never be assessed.

Instead of waiting for a grade, the users should reset as soon as they finish self-assessment.

This does imply that we'll need some submissions in the database before running a performance test.  If we were to start with 0 submissions, then there wouldn't be enough submissions available to peer-assess, and users wouldn't get to the self-assessment step.