Drop use of 'oslo' namespace package

The Oslo libraries have moved all of their code out of the 'oslo'
namespace package into per-library packages. The namespace package was
retained during kilo for backwards compatibility, but will be removed by
the liberty-2 milestone. This change removes the use of the namespace
package, replacing it with the new package names.

The patches in the libraries will be put on hold until application
patches have landed, or L2, whichever comes first. At that point, new
versions of the libraries without namespace packages will be released as
a major version update.

Please merge this patch, or an equivalent, before L2 to avoid problems
with those library releases.

Blueprint: remove-namespace-packages
https://blueprints.launchpad.net/oslo-incubator/+spec/remove-namespace-packages

Change-Id: Iae62b48993eef3b31420f8cc245a55f5e303c4fc

designate/storage/impl_sqlalchemy/__init__.py

@@ -16,7 +16,7 @@
 import time
 import hashlib
 
-from oslo.config import cfg
+from oslo_config import cfg
 from oslo_log import log as logging
 from oslo_db import options
 from sqlalchemy import select, distinct, func