This option, along with monkey_patch_modules, is
arguably worse than hooks since it doesn't even
rely on having in-tree code. It's super legacy,
not tested, not supported and is a barrier to
interoperability, so we should deprecate it for
removal.
This also allows us to deprecate the default_publisher_id
option which is used for the legacy notify_decorator
which is only used if specified with the monkey_patch_modules
option, which is also deprecated here.
Also removed the nova.api.ec2.cloud mention from the
config option help text for monkey_patch_modules
since that isn't valid in nova anymore.
Change-Id: Id793ac2c5cdc5dc473f95eac53b77617a1e389da