Use oslo.versioned_object in websocket proxy

[hongbin]

In websocket module (https://github.com/openstack/zun/blob/master/zun/websocket/websocketproxy.py), it uses db_api directly (line #35: from zun.db import api as db_api). It is better to use object (https://github.com/openstack/zun/blob/master/zun/objects/container.py) instead. This is because oslo.object provides many benefits (i.e. rolling upgrade).

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/565409

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/565409
Committed: https://git.openstack.org/cgit/openstack/zun/commit/?id=caacd056701e21a713625c9a24c561466bef8103
Submitter: Zuul
Branch: master

commit caacd056701e21a713625c9a24c561466bef8103
Author: Hongbin Lu <email address hidden>
Date: Tue May 1 03:59:40 2018 +0000

    Use versioned object instead of db_api

    In websocket proxy module, it directly used db_api to retrieve the
    container. It is better to use versioned object instead since
    versioned object has several benenfits, such as support upgrade.

    Change-Id: Ic8697f4a3fe3ed522fea802225061004203952ad
    Closes-Bug: #1766132

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/zun 2.0.0 release.