Add initial framing of placement API

The placement API will initially host resource provider
information and then will grow to provide a full placement
service. Eventually it will be fully extracted from Nova.

To facilitate that extraction, this service is being developed
with few ties to existing nova.wsgi structures. Instead it
uses relatively plain WSGI apps that are:

* uses the Routes library with declarative mapping defined in
  ROUTE_DECLARATIONS
* basic wsgi apps, with webob and the request class, for each handler
  define as functions
* does not use a paste-ini file to compose middleware, instead code
  which minimally inspects the oslo config to know how to adjust
  middleware (in the initial case choosing an auth_strategy)

Many of these "features" will be demonstrated in commits that
follow this one that enable specific behaviors for resource
providers and their inventories.

In order to ensure that this change can be merged in an atomic
fashion it includes microversion support that was previously in its
own commit.

The microversion_parse library is used in a WSGI middleware
to parse incoming microversion headers and place the
determined value into the WSGI environment at the
'placement.microversion' key. Response headers are adjusted to
add the required outgoing headers as described in:

http://specs.openstack.org/openstack/api-wg/guidelines/microversion_specification.html

If a client requests an invalid microversion, they will receive
a 400 response. If the microversion is of a valid form but not
available, they will received a 406 response. The format of that
response is dependent on the accept header of the request. If it
is JSON, the min and max available microversions are presented.

A request to '/' will return version discovery information.

Thus far nothing else is done with the microversion information.
It is there for when we need it in the future. For now everything
is version 1.0.

The groundwork for using gabbi to test the API is in place in
nova/tests/functional/api/openstack/placement. The gabbi tests
are included in the functional target. To run just the placement
tests it is possible to run 'tox -efunctional placement'.

Change-Id: Icb9c8f7a1fa8a9eac66c2d72f4b7e4efd4e1944f
Partially-Implements: blueprint generic-resource-pools

nova/api/openstack/placement/placement-api.py

@@ -0,0 +1,27 @@
+#    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.
+"""WSGI script for Placement API
+
+WSGI handler for running Placement API under Apache2, nginx, gunicorn etc.
+"""
+
+from nova.api.openstack.placement import deploy
+from nova import conf
+from nova import config
+
+
+CONFIG_FILE = '/etc/nova/nova.conf'
+
+
+config.parse_args([], default_config_files=[CONFIG_FILE])
+
+application = deploy.loadapp(conf.CONF)