Nova volume update fails if swapping a volume more than once on the same connection

[Ryan McNair]

Description
=======================
Using "nova volume update" will only succeed the first time when called on a particular connection.

Steps to Reproduce
=======================
This was found while creating test coverage for swap volume, so the exact reproduce steps are in the Tempest test https://review.openstack.org/#/c/258593/, but to sum it up

1) Create server
2) Create vol A and attach to server
3) Create vol B
4) nova volume update server <A> <B>
5) nova volume update server <B> <A> (this will fail

Expected Result
=====================
Should be able to swap two volumes, then swap them back to get to the original state

Actual Result
=====================
After swapping two volumes, any attempt to swap them back will fail while grabbing the BDM (https://github.com/openstack/nova/blob/master/nova/virt/libvirt/driver.py#L1414)

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/304714

[Matt Riedemann (mriedem)]

Is this a duplicate of bug 1490236 ?

[OpenStack Infra (hudson-openstack)]

Change abandoned by Ryan McNair (<email address hidden>) on branch: master
Review: https://review.openstack.org/304714
Reason: Abandoning in favor of https://review.openstack.org/#/c/257135/