Bug 1877222

Description of problem:

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After create a multiattach volume in RHOSP16.1 , we cannot assign the volume to more than one VM via dashboard.
However, we can use CLI like "nova volume-attach" to attach the multiattach volume to more then one VM.
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Version-Release number of selected component (if applicable):
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# sudo podman ps | grep horizon
5773a10ea430  manager.ctlplane.localdomain:8787/rhosp-rhel8/openstack-horizon:16.1-51                    kolla_start           5 days ago    Up 5 days ago           horizon

# rpm -qa |grep horizon
puppet-horizon-15.4.1-0.20200604003425.dd78e01.el8ost.noarch
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How reproducible:

Use the dashboard to assign multiattach volume to one VM; then create another VM and try to attach the volume, you cannot see the volume in dropdown list.
The volume can only be assigned to one VM.

Steps to Reproduce:
1. Use the dashboard to assign multiattach volume to one VM
2. Create another VM and try to attach the volume 
3. We cannot see the volume in the dropdown list.

Actual results:
We cannot use dashboard to assign multiattach volume to more then one VM.

Expected results:
We can use dashboard to assign multiattach volume to more then one VM.

Additional info:
It seems that we have commits for "multiattach"; maybe we need to double check the detail against dashboard.
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# podman run -it --rm openstack-horizon:16.1-51 bash
()[root@24af034e4eef /]# cd /usr/lib/python3.6/site-packages/openstack_dashboard/
()[root@24af034e4eef openstack_dashboard]# sed -n '90,94p' api/cinder.py 
              'snapshot_id', 'source_volid', 'attachments', 'tenant_name',
              'group_id', 'consistencygroup_id', 'os-vol-host-attr:host',
              'os-vol-tenant-attr:tenant_id', 'metadata',
              'volume_image_metadata', 'encrypted', 'transfer',
              'multiattach']
              
()[root@24af034e4eef openstack_dashboard]# sed -n '30,40p' api/microversions.py 
    "nova": {
        "locked_attribute": ["2.9", "2.42"],
        "instance_description": ["2.19", "2.42"],
        "remote_console_mks": ["2.8", "2.53"],
        "servergroup_soft_policies": ["2.15", "2.60"],
        "servergroup_user_info": ["2.13", "2.60"],
        "multiattach": ["2.60"],
        "auto_allocated_network": ["2.37", "2.42"],
        "key_types": ["2.2", "2.9"],
        "key_type_list": ["2.9"],
    },
    
()[root@24af034e4eef openstack_dashboard]# sed -n '5652,5678p' dashboards/project/instances/tests.py 
    @mock.patch.object(api.cinder, 'volume_list')
    @mock.patch.object(api.cinder, 'volume_get')
    @mock.patch.object(api.nova, 'get_microversion', return_value='2.60')
    @mock.patch.object(api._nova, 'novaclient')
    def test_volume_attach_post_multiattach(
            self, mock_client, mock_get_microversion, mock_volume_get,
            mock_volume_list):
        # Tests that a multiattach volume must be attached with compute API
        # microversion 2.60 and the feature is supported.
        server = self.servers.first()
        volumes = self.cinder_volumes.list()
        volume = volumes[1]
        volume.multiattach = True
        mock_volume_list.return_value = volumes
        mock_volume_get.return_value = volume

        # note that 'device' is not passed
        form_data = {"volume": volume.id,
                     "instance_id": server.id}

        url = reverse('horizon:project:instances:attach_volume',
                      args=[server.id])

        res = self.client.post(url, form_data)
        self.assertNoFormErrors(res)
        self.assertRedirectsNoFollow(res, INDEX_URL)
        mock_client.assert_called_once_with(mock.ANY, '2.60')
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Regards
Sam