Ensure BFV model allows for multiattach

[Julia Kreger]

One of the outcomes of the Sydney summit feedback, and team discussion of that feedback was that it would be good to enable support for booting multiple nodes from the same target volume.

Constraint wise, we need to ensure two things:
1) That our process does not squash existing attachments
2) That our data model allows for different nodes to have the same target volume.

This is to support the use case where the boot device is likely a block device with a prepared ramdisk that is common amongst a pool of machines. Etherpad from discussion can be found at https://etherpad.openstack.org/p/ironic-queens-midcycle starting at line 67.

[Julia Kreger (juliaashleykreger)]

Findings:

1) Our data model DOES allow for multi-attach.
2) We should have accounted for it accordingly when designing cinder support.

Submitting a patch to the BFV documentation.

[OpenStack Infra (hudson-openstack)]

Fix proposed to branch: master
Review: https://review.openstack.org/526531

[OpenStack Infra (hudson-openstack)]

Reviewed: https://review.openstack.org/526531
Committed: https://git.openstack.org/cgit/openstack/ironic/commit/?id=26d7be52d76e79bd7eb218ded64244b1fc2a612e
Submitter: Zuul
Branch: master

commit 26d7be52d76e79bd7eb218ded64244b1fc2a612e
Author: Julia Kreger <email address hidden>
Date: Thu Dec 7 17:34:28 2017 -0500

    Add documentation covering storage multi-attach

    Change-Id: Ia4767328023acfa43ce513396fc963e75ba60b52
    Closes-Bug: #1735474

[OpenStack Infra (hudson-openstack)]

This issue was fixed in the openstack/ironic 10.0.0 release.