just set necessary config options

There are many warning info in the Watcher api log file,
the reason is that keystonemiddleware only need config
section keystone_authtoken.
refer to https://docs.openstack.org/keystonemiddleware/latest/
Closes-Bug: #1864129

Change-Id: Ie790277d55b3a2d93c26781f7e5e8f66b87227d8

watcher/api/acl.py

@@ -37,5 +37,5 @@ def install(app, conf, public_routes):
     if not CONF.get('enable_authentication'):
         return app
     return auth_token.AuthTokenMiddleware(app,
-                                          conf=dict(conf),
+                                          conf=dict(conf.keystone_authtoken),
                                           public_api_routes=public_routes)