add option to logout on oauth token deletion, fixes CAT-67

test plan:
- do an oauth login, perhaps by using some external app, or by following
  the guide at https://canvas.instructure.com/doc/api/file.oauth.html
- end the oauth session with param expire_sessions=1, i.e.
    DELETE <canvas>/login/oauth2/token?expire_sessions=1
- do another oauth login, and notice that you're asked for your
  credentials.  i.e., your canvas session was destroyed.  that's a good
  thing.

Change-Id: I765d8f62dfcd133bc652b484c26c7bb1fc86e24a
Reviewed-on: https://gerrit.instructure.com/32866
Reviewed-by: Jon Jensen <jon@instructure.com>
Product-Review: Marc LeGendre <marc@instructure.com>
QA-Review: Marc LeGendre <marc@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>