doesn't issue an error log even if libvirt couldn't import

[fujioka yuuichi]

When ImportError occurs, LibvirtInspector throws InstanceNotFoundException.
The ceilometer-agent-compute does not issue an error log even if caught InstanceNotFoundException.
Therefore, ceilometer-agent-compute doesn't issue an error log even if libvirt couldn't import.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/48876

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/48876
Committed: http://github.com/openstack/ceilometer/commit/440bdacec19feef025decd726e8f893c1f2ae02f
Submitter: Jenkins
Branch: master

commit 440bdacec19feef025decd726e8f893c1f2ae02f
Author: fujioka yuuichi <email address hidden>
Date: Mon Sep 30 10:19:12 2013 +0900

    issue an error log when cannot import libvirt

    the ceilometer-compute-agent doesn't issue an error log even if libvirt
    couldn't be imported.

    This patch fixes this problem.

    Change-Id: I91bd80a694983da3eab93866a649a61b09d133c7
    Closes-Bug: #1232961