Logging "None" in place of path in libvirt driver

[Paul Murray]

The get_instance_disk_info method in the nova.virt.libvirt.driver logs a None value if a disk path is undefined. The log message is intended to show a path that does not represent a path, but in the case the path does not actually exist, it gives the following uninformative message:

2013-10-14 06:25:21.404 45722 DEBUG nova.virt.libvirt.driver [-] skipping None since it looks like volume get_instance_disk_info /usr/lib/python2.7/dist-packages/nova/virt/libvirt/driver.py:4299

When the path is not defined it should log the instance it is looking at instead.

[Paul Murray (pmurray)]

The order of two tests for the path existing and the file type can be reversed so that we know the path exists before looking at its type and possibly logging it.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/51663

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/51663
Committed: http://github.com/openstack/nova/commit/c31ae4987c5ae2015cc5379a4717490b75c62c9e
Submitter: Jenkins
Branch: master

commit c31ae4987c5ae2015cc5379a4717490b75c62c9e
Author: Paul Murray <email address hidden>
Date: Mon Oct 14 17:44:20 2013 +0100

    Improve logging messages in libvirt driver

    This is a trivial change to correct an uninformative log message.
    There are two checks in get_instance_disk_info that look at a disk.
    One checks for the type of a disk and logs its path if it is not a file.
    The other checks for the path and logs the instance name it belongs to
    if it does not exist. The first will log None if the path does not exist,
    so reverse the order of the checks.

    Closes-Bug: #1239747
    Change-Id: Ieb52ba0584ad789dc55f40e0172cf5ed41e86fbe