Add 'warning' as an alias to 'warn'

The standard Python logging system uses 'warning' and not 'warn'. To
ease compatibility with it, let's add 'warning' too.

Change-Id: I7778d7960ca7a72be007cb083e5434ede6e3fe6e
notifier: add audit level

This maps what is provided by the openstack.common.logging module.

Change-Id: Id581c4c748e2763a2c9a3e576e3bd497595adbff
Implement a log handler using notifier

Change-Id: Iccac043d46a733e965b3310bbbe9c7d6c07a46ac
Blueprint: logging-and-notification
Avoid storing configuration in notifier

The notifier itself doesn't use the configuration. So let's not store
it, that lights the dependency a bit on this configuration object.

Blueprint: messaging-decouple-cfg

Change-Id: Ic4b5ddd93ea0382bd8292f9e31b7dacba9b489d3
Merge "Avoid storing configuration in notifier"