GlusterFS: allow snapshot_delete when snapshot info does not exist

[Eric Harney]

The snapshot_delete operation will fail if the backing file for the snapshot does not exist. This happens in legitimate cases such as when snapshot_create fails due to permissions problems.

The driver should allow the manager to delete the snapshot in this case where this is no action required for the driver to delete anything.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/57335

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/57335
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=d8a11168c908fe6c6a07fbb30a5bc88a6df6e939
Submitter: Jenkins
Branch: master

commit d8a11168c908fe6c6a07fbb30a5bc88a6df6e939
Author: Eric Harney <email address hidden>
Date: Tue Nov 19 16:25:47 2013 -0500

    GlusterFS: Complete snapshot_delete when info doesn't exist

    The snapshot_delete operation will fail if the snapshot info file
    doesn't contain a record for the snapshot, or does not exist.
    This happens in cases such as when snapshot_create fails to commit
    anything to disk.

    The driver should allow the manager to delete the snapshot
    in this case, as there is no action required for the driver
    to delete anything.

    Closes-Bug: #1252864

    Change-Id: I8686a1be09dbb7984072538bff6c026bb84eeb52

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/havana
Review: https://review.openstack.org/64949