Comment 6 for bug 1629110

Reviewed: https://review.openstack.org/383971
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=4e6958551c324635a8720fc9125e9596860637f7
Submitter: Jenkins
Branch: stable/mitaka

commit 4e6958551c324635a8720fc9125e9596860637f7
Author: Ken'ichi Ohmichi <email address hidden>
Date: Wed Sep 28 17:41:51 2016 -0700

    Fix error status code on update-volume API

    As the following part of API-WG guidline[1],

      If a request contains a reference to a nonexistent resource in the
      body (not URI), the code should be 400 Bad Request. Do not use 404
      NotFound because :rfc:`7231#section-6.5.4` (section 6.5.4) mentions
      the origin server did not find a current representation for the
      target resource for 404 and representation for the target resource
      means a URI

    Nova should return a BadRequest response(400) in this case, because
    new_volume_id is specified in a request body. old_volume_id is not
    necessary to be changed because the value is specified with URI.
    So it is valid to return NotFound response if that is not existent.

    [1]: https://github.com/openstack/api-wg/blob/master/guidelines/http.rst#failure-code-clarifications

    Close-Bug: #1629110
    Change-Id: Ib781b116f5af713d64b5880858cc4f81c3da3977
    (cherry picked from commit edd86d9dac1ea75bc580a7964e7d699ee9644b19)