Modify the test cluster plugin to allow whitelisted users to bypass the student lockout

Modifications to both the sfu_api and test_cluster plugins to allow whitelisted users to bypass the student lockout.

The whitelist is a SFU maillist: canvas-test-cluster-bypass. It's currently owned by me but it should be handed off to someone else, probably within the TLC.

This code (along with a current database) is installed on icat-graham-canvas.its.sfu.ca. Test steps below; when logging in as someone else, use the yourusername:theirusername CAS feature, not the built-in impersonation.

- Log in as yourself (an admin user). You should still have full access to everything.
- Log in as an instructor. You should still have full access to everything inside a course (matches `@context.grants_right?(@current_user, :read_as_admin)`).
- Log in as a student who is not a member of canvas-test-cluster-bypass. You should be able to get to the "front page" of a course, but no further inside the course (matches neither `@context.grants_right?(@current_user, :read_as_admin)` or `SFU::User.belongs_to_maillist?(current_username, "canvas-test-cluster-bypass")`).
- Add the student to the canvas-test-cluster-bypass list and try again. You should not be able to access previously-restricted pages inside the course (matches `SFU::User.belongs_to_maillist?(current_username, "canvas-test-cluster-bypass")`).