load extension lead to error calling 'volumes': 'NoneType' object has no attribute 'controller' for v3 api

[jichenjc]

Add a new plugin lead to following error, the root cause is servers was loaded after volumes
so the inherits.controller is None

if resource.inherits:
                inherits = self.resources.get(resource.inherits)
                if not resource.controller:
                    resource.controller = inherits.controller

ERROR [stevedore.extension] error calling 'volumes': 'NoneType' object has no attribute 'controller'
ERROR [stevedore.extension] 'NoneType' object has no attribute 'controller'
Traceback (most recent call last):
  File "/home/jichen/git/nova/.venv/local/lib/python2.7/site-packages/stevedore/extension.py", line 248, in _invoke_one_plugin
    response_callback(func(e, *args, **kwds))
  File "/home/jichen/git/nova/nova/api/openstack/__init__.py", line 376, in _register_resources
    resource.controller = inherits.controller
AttributeError: 'NoneType' object has no attribute 'controller'
DEBUG [nova.api.openstack] Running _register_resources on <nova.api.openstack.compute.plugins.v3.servers.Servers object at 0xb484d6c>

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/123640

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/123640
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=510d2eb7a61d7524f6e0a203cb81b475a9ba3035
Submitter: Jenkins
Branch: master

commit 510d2eb7a61d7524f6e0a203cb81b475a9ba3035
Author: jichenjc <email address hidden>
Date: Mon Nov 10 05:30:18 2014 +0800

    Load extension 2 times fix load sequence issue

    Some extensions such as volumes need to inherit servers, however
    the extension load sequence can't be guaranted. If the servers
    extension is loaded after volumes, the controller of volumes will
    be None and lead to problem.

    Change-Id: Iec1e759f5c1f570a6b0ac65fb357b4f15102499c
    Closes-Bug: #1373238