osinfo should not emit multiple error messages when module isn't loaded

[Vladik Romanovsky]

Currently osinfo module emits multiple error messages , when libosinfo module cannot be loaded:

2016-02-08 12:44:15.270 2868 ERROR nova.virt.osinfo [req-cb9744f0-c5af-4bc7-a164-6e0ba06c021d tempest-VolumesV1SnapshotTestJSON-1106516754 tempest-VolumesV1SnapshotTestJSON-1593599156] Cannot find OS information - Reason: (Cannot load Libosinfo: (No module named gi.repository.Libosinfo))

Since loading the libosinfo module is optional, It should only report this info once and not as an error message.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/277565

[Matt Riedemann (mriedem)]

There is a devstack change here to install libosinfo from the distro so we actually start using this code in the gate:

https://review.openstack.org/#/c/278142/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/277565
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=556e4944e903a2742226308190fd34bc4ee9984d
Submitter: Jenkins
Branch: master

commit 556e4944e903a2742226308190fd34bc4ee9984d
Author: Vladik Romanovsky <email address hidden>
Date: Mon Feb 8 16:06:41 2016 -0500

    virt: osinfo will report once if libosinfo is not loaded

    Currently osinfo module emits multiple error messages when libosinfo
    module cannot be loaded. Since loading the libosinfo module is optional,
    it should only report this once as an INFO log message.

    Change-Id: If4b582d1ec39ba79b4f993543da11ec8c6bd023b
    Closes-bug: #1543288