Comment 8 for bug 1775418

Reviewed: https://review.opendev.org/662333
Committed: https://git.openstack.org/cgit/openstack/nova/commit/?id=c19d602f9be536ee8412bac0f0951a995424f25e
Submitter: Zuul
Branch: stable/rocky

commit c19d602f9be536ee8412bac0f0951a995424f25e
Author: Matt Riedemann <email address hidden>
Date: Wed Jun 6 10:32:37 2018 -0400

    Block swap volume on volumes with >1 rw attachment

    If we're swapping from a multiattach volume that has more than one
    read/write attachment, another server on the secondary attachment could
    be writing to the volume which is not getting copied into the volume to
    which we're swapping, so we could have data loss during the swap.

    This change does volume read/write attachment counting for the volume
    we're swapping from and if there is more than one read/write attachment
    on the volume, the swap volume operation fails with a 400 BadRequest
    error.

    Conflicts:
          nova/tests/unit/compute/test_compute_api.py

    NOTE(mriedem): The conflict is due to Stein change
    I7d5bddc0aa1833cda5f4bcebe5e03bdd447f641a changing the
    decorators on the _test_snapshot_and_backup method.

    Depends-On: https://review.openstack.org/573025/
    Closes-Bug: #1775418
    Change-Id: Icd7fcb87a09c35a13e4e14235feb30a289d22778
    (cherry picked from commit 5a1d159d142997bb4288d4bf86d4e144334905cd)
    (cherry picked from commit 9b21d1067a071ab17758068dfca5cd2ebd29d868)