Re-Add oslo.middleware namespace for backward compat

Short Story:
If we don't do this then we have to drop,
assert:support-upgrade from nova (Really Really Bad!)

Longer Story:
We need to support kilo paste-ini until liberty-eol per policies
already in place. To do that an alternative would have been
to cap global-requirements, but that got ruled out, please
see work and reasons here:
I5731b0278e266699fe716733b6dd4f7238a35586

There's also another new spec openstack-specs that is gathering
a lot of positive votes regarding backward compat:
I72e4e9cfa0539f6b326a0296c065fa3cb754f8ae

Note that this is not a straight revert of:
I1479f37f500a358cdf7ad416f0257288b65c9245

As i just want to drop the tests and keep the files to a
minimum. The grenade job is enough to test the older
scenario (which was failing) which we need to support.

Change-Id: I04739bc3987786b4bc1fefc70fabaa69b3de52b4
Closes-Bug: 1524404

oslo/__init__.py

@@ -0,0 +1,13 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+__import__('pkg_resources').declare_namespace(__name__)

oslo/middleware/__init__.py

@@ -0,0 +1,42 @@
+#    Licensed under the Apache License, Version 2.0 (the "License"); you may
+#    not use this file except in compliance with the License. You may obtain
+#    a copy of the License at
+#
+#         http://www.apache.org/licenses/LICENSE-2.0
+#
+#    Unless required by applicable law or agreed to in writing, software
+#    distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+#    WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+#    License for the specific language governing permissions and limitations
+#    under the License.
+
+import sys
+import warnings
+
+def deprecated():
+    new_name = __name__.replace('.', '_')
+    warnings.warn(
+        ('The oslo namespace package is deprecated. Please use %s instead.' %
+         new_name),
+        DeprecationWarning,
+        stacklevel=3,
+    )
+
+
+# NOTE(dims): We cannot remove the deprecation or redirects below
+# until Liberty-EOL
+deprecated()
+
+from oslo_middleware import base
+from oslo_middleware import catch_errors
+from oslo_middleware import correlation_id
+from oslo_middleware import debug
+from oslo_middleware import request_id
+from oslo_middleware import sizelimit
+
+sys.modules['oslo.middleware.base'] = base
+sys.modules['oslo.middleware.catch_errors'] = catch_errors
+sys.modules['oslo.middleware.correlation_id'] = correlation_id
+sys.modules['oslo.middleware.debug'] = debug
+sys.modules['oslo.middleware.request_id'] = request_id
+sys.modules['oslo.middleware.sizelimit'] = sizelimit

setup.cfg

@@ -20,7 +20,11 @@ classifier =
 
 [files]
 packages =
+    oslo
+    oslo.middleware
     oslo_middleware
+namespace_packages =
+    oslo
 
 [entry_points]
 oslo.config.opts =