In some case lose information of the first exception in SwiftBackupDriver

[Kiyohiro Adachi]

When an exception occurs during exception handling, it lose the
information of the first exception.

In SwiftBackupDriver.backup(), in some cases, before re-transmission
of the exception, the exception is rewritten.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/80502

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/80502
Committed: https://git.openstack.org/cgit/openstack/cinder/commit/?id=3f67de92cfcfc61ca26156961e1f2d4d2ebded66
Submitter: Jenkins
Branch: master

commit 3f67de92cfcfc61ca26156961e1f2d4d2ebded66
Author: KIYOHIRO ADACHI <email address hidden>
Date: Fri Mar 14 16:04:57 2014 +0900

    Fix unsaved exception in backup/drivers

    When an exception occurs during exception handling, it loses the
    information of the first exception.

    We should use the excutils.save_and_reraise_exception() in some cases.

    Change-Id: I5d0ea53ba6c52138c71cca61aedbdf06338f2a7d
    Closes-Bug: #1292380