Test logging out old users in data8x
Test logging out old users in data8x

Tests https://github.com/jupyterhub/ltiauthenticator/pull/31

data8x has different 'courses' in EdX that create different
'users' in JupyterHub. This causes problems - if a user logs in
from one course, they won't get logged into the *correct* course
when they log in from another course!

This would log them out of the last session when they log in
as a new user.

Ref #1725

ryanlovett/datahub,ryanlovett/datahub,ryanlovett/datahub,berkeley-dsep-infra/datahub,berkeley-dsep-infra/datahub,berkeley-dsep-infra/datahub