Placement api: set custom json_error_formatter in root

Change decorator for resource based actions in root
handler to wsgi_wrapper.PlacementWsgify

This is a newly introduced wrapper class around webob.dec.wsgify
to set json formatter in case of webob exceptions.

Change-Id: I847345f7f15a46930faf8793baf801beba98d368
Closes-Bug: #1635182

nova/api/openstack/placement/handlers/root.py

@@ -13,13 +13,13 @@
 
 from oslo_serialization import jsonutils
 from oslo_utils import encodeutils
-import webob
 
 
 from nova.api.openstack.placement import microversion
+from nova.api.openstack.placement import wsgi_wrapper
 
 
-@webob.dec.wsgify
+@wsgi_wrapper.PlacementWsgify
 def home(req):
     min_version = microversion.min_version_string()
     max_version = microversion.max_version_string()

nova/tests/functional/api/openstack/placement/gabbits/microversion.yaml

@@ -36,6 +36,8 @@ tests:
       $.errors.[0].min_version: /^\d+\.\d+$/
   response_strings:
       - "Unacceptable version header: 0.5"
+  response_json_paths:
+      $.errors[0].title: Not Acceptable
 
 - name: latest microversion is 1.4
   GET: /
@@ -63,6 +65,8 @@ tests:
   status: 400
   response_strings:
       - "invalid version string: pony.horse"
+  response_json_paths:
+      $.errors[0].title: Bad Request
 
 - name: bad format multidot raises 400
   GET: /
@@ -71,6 +75,8 @@ tests:
   status: 400
   response_strings:
       - "invalid version string: 1.2.3"
+  response_json_paths:
+      $.errors[0].title: Bad Request
 
 - name: error in application produces microversion headers
   desc: we do not want xml