GlusterFS clone from snapshot may select wrong source file

[Eric Harney]

_copy_volume_from_snapshot appears to select its source file using _local_path_volume but needs to resolve source file by using the snap_info metadata.

Found this while filling in gaps in the unit test code, will add tests to cover this.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/46763

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/46763
Committed: http://github.com/openstack/cinder/commit/867b131e09a43ba7ed36267dcdec751abd652f14
Submitter: Jenkins
Branch: master

commit 867b131e09a43ba7ed36267dcdec751abd652f14
Author: Eric Harney <email address hidden>
Date: Mon Sep 9 18:47:00 2013 -0400

    GlusterFS: Copy snap from correct source file

    The GlusterFS driver's copy_volume_from_snapshot was previously
    not parsing the snapshot information to determine which backing
    file to copy from, instead copying from the active file at all
    times. This would result in the wrong data being supplied when
    a volume is cloned from a snapshot.

    Add a test for the copy_volume_from_snapshot method.

    Closes-Bug: #1222907
    Change-Id: Ib829ca1a6812b61845f3b2eb9c5507779fa6ec15