cinder backup should use pipe for diff transfer

[Edward Hope-Morley]

When the cinder ceph backup driver attempts a differential transfer, the diff is held in memory. This will rapidly become a problem e.g. for bootable volumes, resulting in memory allocation errors.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/53923

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/53923
Committed: http://github.com/openstack/cinder/commit/d384d28e1c2c7c3ce0bd676fb1c2bdb8a2d98a03
Submitter: Jenkins
Branch: master

commit d384d28e1c2c7c3ce0bd676fb1c2bdb8a2d98a03
Author: Edward Hope-Morley <email address hidden>
Date: Fri Oct 25 10:57:55 2013 -0700

    Use pipe between ceph backup diff export/import

    We now use a piped transfer between the rbd export-diff
    and import-diff for incremental backups/restores as
    opposed to holding the entire diff in memory.

    Change-Id: I33476d9b3934781413af5cd2867a11d825a5d78e
    Fixes: bug 1244464

[Edward Hope-Morley (hopem)]

Now that this has been appoved, I will nominate it for backport to stable/havana

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: stable/havana
Review: https://review.openstack.org/54589

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/54589
Committed: http://github.com/openstack/cinder/commit/022f1df261d15ca8faa89382974e772473bce69d
Submitter: Jenkins
Branch: stable/havana

commit 022f1df261d15ca8faa89382974e772473bce69d
Author: Edward Hope-Morley <email address hidden>
Date: Fri Oct 25 10:57:55 2013 -0700

    Use pipe between ceph backup diff export/import

    We now use a piped transfer between the rbd export-diff
    and import-diff for incremental backups/restores as
    opposed to holding the entire diff in memory.

    Change-Id: I33476d9b3934781413af5cd2867a11d825a5d78e
    Fixes: bug 1244464
    (cherry picked from commit d384d28e1c2c7c3ce0bd676fb1c2bdb8a2d98a03)