zaqar-wsgi raise 500 error when create a pool

[wangxiyuan]

reproduce:
1. create a pool with url : "uri": "mongodb://localhost:27017",
2.create an other pool with the same url.

Zaqar-wsgi will return 500 error.

The reason is that Zaqar-wsgi doesn't catch DuplicateKeyError for pymongo.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/274537

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/274537
Committed: https://git.openstack.org/cgit/openstack/zaqar/commit/?id=ad47f1bcfc4e10ef2261432f58a247244fdad980
Submitter: Jenkins
Branch: master

commit ad47f1bcfc4e10ef2261432f58a247244fdad980
Author: wangxiyuan <email address hidden>
Date: Mon Feb 1 15:45:33 2016 +0800

    Fix 500 error when create pools in wsgi v2.

    When create a pool with a url which is already exist in db,
    pymongo will raise a DuplicateKeyError error. Zaqar-wsgi
    don't catch it.

    APIImpact

    Change-Id: I487a372533c5e8de9edd5796e0039320d2d55b6a
    Closes-bug: #1540246