update canvas_connect to use fake email addresses.

fixes CNVS-5723

to avoid username conflicts, create users with usernames in
the format of canvas_{global_id}@instructure.com.
use unique canvas emails to avoid conflicts.

append email addresses with "+canvas-#{uuid}" to solve
problem where existing connect users who shared an email
address with their canvas account could not log in.

test plan:
  * attempt to create/join an adobe connect conference
    and verify that it works as expected.