Comment 12 for bug 1842930

Added Keystonemiddleware and documentation tags. Marked as "medium" importance as it requires documentation changes but is not critical/RC/otherwise impacting. Clear communication of expected behavior is important and should be found in Horizon and Keystonemiddleware's documentation.

I am marking invalid for Keystone itself as keystone will invalidate it's internal cache (barring cases such as in-memory [not production quality] dict-base cache).