Don't replace the whole app just the wsgi_app backing

Do not replace the entire app when wrapping with middleware. It is
important to maintain all the flask-functionality on the app object
and ensure any/all test client calls go through the entire stack of
app and middleware.

Partial-Bug: #1776504
Change-Id: I928d08e96b4c79807ad8c312ba17359c54b67fa0

keystone/server/flask/application.py

@@ -230,7 +230,7 @@ def application_factory(name='public'):
                                  rtr in ALL_API_ROUTERS]):
         dispatch_map['/v3/%s' % pfx] = legacy_dispatcher
 
-    application = KeystoneDispatcherMiddleware(
-        app,
+    app.wsgi_app = KeystoneDispatcherMiddleware(
+        app.wsgi_app,
         dispatch_map)
-    return application
+    return app

keystone/server/flask/core.py

@@ -122,10 +122,10 @@ def setup_app_middleware(app):
         # local_conf, this is all a hold-over from paste-ini and pending
         # reworking/removal(s)
         factory_func = loaded.driver.factory({}, **mw.conf)
-        app = factory_func(app)
+        app.wsgi_app = factory_func(app.wsgi_app)
 
     # Apply werkzeug speficic middleware
-    app = fixers.ProxyFix(app)
+    app.wsgi_app = fixers.ProxyFix(app.wsgi_app)
     return app