oslo.policy emits a deprecation warning for every single rule that we
have deprecated at least once when a request comes in, and possibly
subsequent times if keystone is running in multiple processes, and even
more after keystone is reloaded. It's not useful to repeat nearly
identical multi-line messages for each policy every time: logs aren't
meant to justify our reasoning, they're just meant to be informative.
The relevant information and rationalization can be found in the release
notes. Repeating these identical multi-line messages starts to use up
space quickly and makes the logs unreadable.
This patch reduces the DEPRECATED_REASON for each policy to one brief
line, which should help make the logs more readable in general and
especially when run in a multiprocess environment, reduce the disk
footprint of the logs, and help with log indexing.