We now expect context objects to support returning a redacted copy of
themselves.
As a related cleanup, removed the practice entirely of using
dictionaries to represent contexts in unit tests and the logging driver.
As part of developing this change, I discovered code in Glance (and
potentially other services) which explicitly pass {} in lieu of a
context when notifying; so we now properly handle dictionaries as
contexts.
To ensure we have the method required; require oslo.context 5.3.0 or
newer.
Change-Id: I894f38cc83c98d3e8d48b59864c0c7c2d27e7dcd
800c58826e