add student single exercise question tests and fix ChangeLocalUserPasswordTest

The following adds two tests related to student exercises:
1. Test that points are added and shown to the student if they get an answer correct.
2. Test that points are not added and do not change if the answer is wrong.

Some utility functions have been added to KALiteDistributedBrowserTestCase:
1. db_create_student = insert a FacilityUser directly into the database instead of using a browser to create one;
2. db_create_facility = insert a Facility into the DB

This also fixes and splits the test found in ChangeLocalUserPassword into two tests:
1. Test that running changelocalpassword on an existing user changes said user's password randomly;
2. Test that running changelocalpassword on a nonexistent user returns