Description of problem: When I try to live migrate (retype) an attached encrypted volume from a netapp(iscsi) backend to Ceph backend, migration doesn't do anything volume remains on netapp backend, no notification\warning on cli. 


Version-Release number of selected component (if applicable):
puppet-cinder-15.4.1-1.20200831153423.el8ost.noarch
openstack-cinder-15.3.1-5.el8ost.noarch
python3-cinder-15.3.1-5.el8ost.noarch
python3-cinderclient-5.0.1-1.20200326150227.8fa0882.el8ost.noarch


How reproducible:
I suspect every time


Steps to Reproduce:
1. Create both types/backend:

(overcloud) [stack@undercloud-0 ~]$ cinder type-create encnetapp
+--------------------------------------+-----------+-------------+-----------+
| ID                                   | Name      | Description | Is_Public |
+--------------------------------------+-----------+-------------+-----------+
| 65baeac5-69fa-4780-be9a-c9265da58e25 | encnetapp | -           | True      |
+--------------------------------------+-----------+-------------+-----------+
(overcloud) [stack@undercloud-0 ~]$ cinder type-create encceph
+--------------------------------------+---------+-------------+-----------+
| ID                                   | Name    | Description | Is_Public |
+--------------------------------------+---------+-------------+-----------+
| bcf9e784-b5c1-406d-a232-0b14c092ea73 | encceph | -           | True      |
+--------------------------------------+---------+-------------+-----------+
(overcloud) [stack@undercloud-0 ~]$ cinder encryption-type-create --cipher aes-xts-plain64 --key_size 256   --control_location front-end encnetapp nova.volume.encryptors.luks.LuksEncryptor
+--------------------------------------+-------------------------------------------+-----------------+----------+------------------+
| Volume Type ID                       | Provider                                  | Cipher          | Key Size | Control Location |
+--------------------------------------+-------------------------------------------+-----------------+----------+------------------+
| 65baeac5-69fa-4780-be9a-c9265da58e25 | nova.volume.encryptors.luks.LuksEncryptor | aes-xts-plain64 | 256      | front-end        |
+--------------------------------------+-------------------------------------------+-----------------+----------+------------------+
(overcloud) [stack@undercloud-0 ~]$ cinder encryption-type-create --cipher aes-xts-plain64 --key_size 256   --control_location front-end encceph nova.volume.encryptors.luks.LuksEncryptor
+--------------------------------------+-------------------------------------------+-----------------+----------+------------------+
| Volume Type ID                       | Provider                                  | Cipher          | Key Size | Control Location |
+--------------------------------------+-------------------------------------------+-----------------+----------+------------------+
| bcf9e784-b5c1-406d-a232-0b14c092ea73 | nova.volume.encryptors.luks.LuksEncryptor | aes-xts-plain64 | 256      | front-end        |
+--------------------------------------+-------------------------------------------+-----------------+----------+------------------+
(overcloud) [stack@undercloud-0 ~]$ cinder service-list
+------------------+---------------------------+------+---------+-------+----------------------------+-----------------+
| Binary           | Host                      | Zone | Status  | State | Updated_at                 | Disabled Reason |
+------------------+---------------------------+------+---------+-------+----------------------------+-----------------+
| cinder-backup    | controller-1              | nova | enabled | up    | 2021-02-09T10:29:58.000000 | -               |
| cinder-scheduler | controller-0              | nova | enabled | up    | 2021-02-09T10:29:54.000000 | -               |
| cinder-scheduler | controller-1              | nova | enabled | up    | 2021-02-09T10:30:02.000000 | -               |
| cinder-scheduler | controller-2              | nova | enabled | up    | 2021-02-09T10:29:56.000000 | -               |
| cinder-volume    | hostgroup@tripleo_ceph    | nova | enabled | up    | 2021-02-09T10:29:56.000000 | -               |
| cinder-volume    | hostgroup@tripleo_netapp2 | nova | enabled | up    | 2021-02-09T10:29:53.000000 | -               |
+------------------+---------------------------+------+---------+-------+----------------------------+-----------------+

(overcloud) [stack@undercloud-0 ~]$ cinder type-key encceph set volume_backend_name=tripleo_ceph
(overcloud) [stack@undercloud-0 ~]$ cinder type-key encnetapp set volume_backend_name=tripleo_netapp2

2. Create an encrypted netapp backed volume:

(overcloud) [stack@undercloud-0 ~]$ cinder create 1 --name encnetappvol1   --volume-type encnetapp 
+--------------------------------+--------------------------------------+
| Property                       | Value                                |
+--------------------------------+--------------------------------------+
| attachments                    | []                                   |
| availability_zone              | nova                                 |
| bootable                       | false                                |
| consistencygroup_id            | None                                 |
| created_at                     | 2021-02-09T10:35:43.000000           |
| description                    | None                                 |
| encrypted                      | True                                 |
| id                             | 9426bce0-889f-4319-a6b6-c5347351d108 |
| metadata                       | {}                                   |
| migration_status               | None                                 |
| multiattach                    | False                                |
| name                           | encnetappvol1                        |
| os-vol-host-attr:host          | None                                 |
| os-vol-mig-status-attr:migstat | None                                 |
| os-vol-mig-status-attr:name_id | None                                 |
| os-vol-tenant-attr:tenant_id   | 85f44a372e6d49b489829bb6389c85fa     |
| replication_status             | None                                 |
| size                           | 1                                    |
| snapshot_id                    | None                                 |
| source_volid                   | None                                 |
| status                         | creating                             |
| updated_at                     | None                                 |
| user_id                        | 45c2199f364d485f986b6d341c512819     |
| volume_type                    | encnetapp                            |
+--------------------------------+--------------------------------------+
(overcloud) [stack@undercloud-0 ~]$ cinder list
+--------------------------------------+-----------+---------------+------+-------------+----------+--------------------------------------+
| ID                                   | Status    | Name          | Size | Volume Type | Bootable | Attached to                          |
+--------------------------------------+-----------+---------------+------+-------------+----------+--------------------------------------+
| 9426bce0-889f-4319-a6b6-c5347351d108 | available | encnetappvol1 | 1    | encnetapp   | false    |                                      |

3. Attach volume to instance:

(overcloud) [stack@undercloud-0 ~]$ nova volume-attach 7137e3a2-9745-4457-bbf4-60cc3c07fb92 9426bce0-889f-4319-a6b6-c5347351d108
+-----------------------+--------------------------------------+
| Property              | Value                                |
+-----------------------+--------------------------------------+
| delete_on_termination | False                                |
| device                | /dev/vde                             |
| id                    | 9426bce0-889f-4319-a6b6-c5347351d108 |
| serverId              | 7137e3a2-9745-4457-bbf4-60cc3c07fb92 |
| tag                   | -                                    |
| volumeId              | 9426bce0-889f-4319-a6b6-c5347351d108 |
+-----------------------+--------------------------------------+

(overcloud) [stack@undercloud-0 ~]$ cinder list
+--------------------------------------+-----------+---------------+------+-------------+----------+--------------------------------------+                                                                                                  
| ID                                   | Status    | Name          | Size | Volume Type | Bootable | Attached to                          |                                                                                                  
+--------------------------------------+-----------+---------------+------+-------------+----------+--------------------------------------
| 9426bce0-889f-4319-a6b6-c5347351d108 | in-use    | encnetappvol1 | 1    | encnetapp   | false    | 7137e3a2-9745-4457-bbf4-60cc3c07fb92 


4. Issue the retype command:

(overcloud) [stack@undercloud-0 ~]$ cinder retype  9426bce0-889f-4319-a6b6-c5347351d108 ceph --migration-policy on-demand

Notice no error or warning. 

5. Volume remains on source/netapp backend:

(overcloud) [stack@undercloud-0 ~]$ cinder list
+--------------------------------------+-----------+---------------+------+-------------+----------+--------------------------------------+
| ID                                   | Status    | Name          | Size | Volume Type | Bootable | Attached to                          |
+--------------------------------------+-----------+---------------+------+-------------+----------+--------------------------------------+
| 9426bce0-889f-4319-a6b6-c5347351d108 | in-use    | encnetappvol1 | 1    | encnetapp   | false    | 7137e3a2-9745-4457-bbf4-60cc3c07fb92 |


Actual results:
Volume doesn't migrate.

Expected results:
if supported, volume should migrate,
else we should block/warn user of trying this. 

Additional info: