The example_user() function is specifically designed for
AARON, hamlet, cordelia, and friends, and it allows a concise
way of using their built-in user profiles. Eventually, the
widespread use of example_user() should help us with refactorings
such as moving the tests users out of the "zulip.com" realm
and deprecating get_user_profile_by_email.
Modify `bot_owner_user_ids()` to return the user_ids of only
admins and bot owners instead of all the current active users.
This was causing a traceback on the frontend.
Fixes: #3391.
This makes get_stream match get_realm, get_user_profile_by_email,
etc., in interface, and is more convenient for mypy annotations
because `get_stream` now doesn't return an Optional[Stream].
Change applies to both subdomains and non-subdomains case, though we use
just the EXTERNAL_HOST in the non-subdomains case if there is only 1 realm.
Fixes#3903.
Steve Howell
Aditya Bansal
Harshit Bansal
Akash Kothawale
Umair Khan
Tim Abbott
Rishi Gupta