remove uncessary log.exception in api layer

[jichenjc]

There are some LOG.exception in api layer, which is not necessary , we should downgrade them

[jichenjc (jichenjc)]

Sorry, I have to mention I am talking about attach_interfaces.py
which log exception when attach can't find a resource

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/95061

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/95061
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=1b46f86148c0366770065fc481984adc6bce5693
Submitter: Jenkins
Branch: master

commit 1b46f86148c0366770065fc481984adc6bce5693
Author: jichenjc <email address hidden>
Date: Fri May 16 05:59:45 2014 +0800

    Downgrade log when attach interface can't find resources

    Downgrade the log when a resource (e.g. instance is deleted concurrently)
    can't be found, no need to LOG.exception because an exception
    is already raised and no need to log again.

    Change-Id: I260e89c8deab11bc9707abbbbc7bb9a4f88640e3
    Closes-Bug: #1322410