log messages around not having python-libguestfs installed need improvement

[Tom Fifield]

Installing havana just now, I ran into some real strange errors about mounting problems.

Thanks to Michael Still, we figured out that this was because libguestfs was not installed it was falling back to do insecure mounts and failing.

A better log message about this fallback, alerting operators of the potential that they don't have appropriate dependencies installed would be appreciated by operators.

[Tom Fifield (fifieldt)]

Example log with the fallback: http://paste.openstack.org/show/48534/

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/110655
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=5be2e456c06bd35ff96066711ee4bbfd1cafe50a
Submitter: Jenkins
Branch: master

commit 5be2e456c06bd35ff96066711ee4bbfd1cafe50a
Author: Jon Grimm <email address hidden>
Date: Wed Jul 30 00:46:57 2014 +0000

    Improve logging when python-guestfs/libguestfs isn't working

    Bumped from debug to warn level, as most often refers to
    missing python-guestfs package or other libguestfs misconfiguration,
    and the fallback path is usually not desired.

    Closes-bug: 1240339
    Change-Id: I5d90a3ea109e79fe17221c001f94d49d599048ba