Fix 'student' refs in grade tests.
Fix 'student' refs in grade tests.

zqian/gradecraft-development,zqian/gradecraft-development,mkoon/gradecraft-development,peterkshultz/gradecraft-development,mkoon/gradecraft-development,UM-USElab/gradecraft-development,UM-USElab/gradecraft-development,mkoon/gradecraft-development,peterkshultz/gradecraft-development,zqian/gradecraft-development,UM-USElab/gradecraft-development,UM-USElab/gradecraft-development,peterkshultz/gradecraft-development