Refactor some mogan exception catch and raise

[wanghao]

Now in some process, Mogan catch the exception and then raise a new wsme.exc.ClientSideError with an additional http_code, but Mogan has defined the http_code in some exception.

So we didn't need raise a new exception, just raise the mogan exception if it has the http_code.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/475971

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/475971
Committed: https://git.openstack.org/cgit/openstack/mogan/commit/?id=ad83d1be16b896ae5399b52b9300c0c2f83ad1f4
Submitter: Jenkins
Branch: master

commit ad83d1be16b896ae5399b52b9300c0c2f83ad1f4
Author: wanghao <email address hidden>
Date: Wed Jun 21 09:11:07 2017 +0800

    Refactor exception raise by using mogan exception

    Now in some process, Mogan catch the exception and
    then raise a new wsme.exc.ClientSideError with an
    additional http_code, but Mogan has defined the
    http_code in some exception.

    So we didn't need raise a new exception,
    just raise the mogan exception if it has the http_code.

    Change-Id: I9150301a43046af8a2e7290ccfebad8ca4118f90
    Close-Bug: #1699075