failed to attach a volume with multiattach to an ironic instance

[Simon Li]

Description
It's no supported that attaches a volume has `multiattach` set to an ironic instance.
It is supported if the volume set `multiattach` to `false`.
Additionally,the storage back end for the volume has `multiattach` property.

Steps to reproduce:
* attach a multiattach volume to an ironic instance.
`openstack --os-compute-api-version 2.60 server add volume <server-uuid> <volume-uuid>`

Expected result
The volume is attached to the server on /dev/*

Actual result
Volume <uuid> has 'multiattach' set, which is not supported for this instance. (HTTP 409)

Environment
* nova:18.2.4
* cinder: 13.0.8
* ironic: 11.1.3
* storage type: G2 Series block storage of Inspur Inc.
* the volume is available state.
* the instance is active and power on.
* the baremetal volume connector has been created and can be sure is available.

More
* Logs of nova-compute for ironic:
ERROR oslo_messaging.rpc.server [req-17d65e1f-0db3-442c-87eb-57d94ffa6940 421c1e16837b4189b9a6ae04ba4af86b 6e3d2c325bc94a5e8dbb41a7a73ae593 - default default] Exception during message handling: nova.exception.MultiattachNotSupportedByVirtDriver: Volume 3e9b3371-d56d-4b16-a180-00b835993662 has 'multiattach' set, which is not supported for this instance.

[Lee Yarwood (lyarwood)]

Volume multiattach is clearly marked as an unsupported feature within the ironic driver [1] so I'm marking this as invalid. If you would like to add support please raise a blueprint and/or spec [2].

[1] https://github.com/openstack/nova/blob/91e53e4c2b90ea57aeac4ec522dd7c8c54961d09/nova/virt/ironic/driver.py#L163
[2] https://docs.openstack.org/nova/latest/contributor/blueprints.html