GlusterFS: Use correct base argument when deleting attached snaps

[Eric Harney]

The base= field is not using the correct value when a libvirt snapshot_delete is issued on the Nova side -- pass correct values for "file_to_merge" in the delete_info dict depending on whether or not other snapshots exist.

This fixes an issue where attached snapshot deletion results in an inconsistent qcow2 chain.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/63223

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/63223
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=186221779a92002ff9fa13c254710c0abb3803be
Submitter: Jenkins
Branch: master

commit 186221779a92002ff9fa13c254710c0abb3803be
Author: Eric Harney <email address hidden>
Date: Wed Dec 18 19:11:44 2013 -0500

    GlusterFS: Use correct base argument when deleting attached snaps

    When deleting the most recent snapshot, the 'file_to_merge' field
    which translates into the base= field for libvirt's blockRebase
    call in Nova must be set depending on whether other snapshots exist.

    If there are no other snapshots, base = None, which results in
    libvirt clearing the qcow2 backing file pointer for the active
    disk image.

    If there are other snapshots, pass the parent of the file being
    deleted as the new base file. The snapshot info pointer for the
    prior base file must also be updated in this case.

    Closes-Bug: #1262880
    Change-Id: If7bc8259b031d0406346caafb8f688e65a38dba6

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/havana
Review: https://review.openstack.org/64950