Various extensions don't respect content header when returning a 202

[Vish Ishaya]

Various nova extensions commands return a text response ("202 Accepted [..]") even when provided with an "Accept: application/json" header. For other 202 responses, either an empty body or a JSON-formatted response is standard. The implementation should be consistent with other 202's from Nova and other OpenStack Services.

This seems to be due to returning a webob exception instead of a response. The affected extensions are:
$ grep HTTPAccepted nova/api/openstack/compute/contrib/*.py
nova/api/openstack/compute/contrib/cloudpipe_update.py: return webob.exc.HTTPAccepted()
nova/api/openstack/compute/contrib/fixed_ips.py: return webob.exc.HTTPAccepted()
nova/api/openstack/compute/contrib/networks_associate.py: return exc.HTTPAccepted()
nova/api/openstack/compute/contrib/networks_associate.py: return exc.HTTPAccepted()
nova/api/openstack/compute/contrib/networks_associate.py: return exc.HTTPAccepted()
nova/api/openstack/compute/contrib/os_networks.py: return exc.HTTPAccepted()
nova/api/openstack/compute/contrib/os_networks.py: return exc.HTTPAccepted()
nova/api/openstack/compute/contrib/os_tenant_networks.py: response = exc.HTTPAccepted()

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/113668

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/113668
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=192d520a22155bd0a2553928da590e7ab8092292
Submitter: Jenkins
Branch: master

commit 192d520a22155bd0a2553928da590e7ab8092292
Author: Vishvananda Ishaya <email address hidden>
Date: Tue Aug 12 15:30:40 2014 -0700

    Fix 202 responses to contain valid content.

    Using a webob.exc to generate 202s makes the response return plain
    text in the body, which breaks things that expect to be able to
    parse data according to the content type. Using a webob.Response
    object makes sure the body of the 202 response is empty.

    Change-Id: Ifca3081f573407808a2196e71ac1db87180db6ec
    Resolves-bug: #1356058