The output of openstack command with `-f value` option has been changed

Issue

• Openstack command result output is inconsistent with previous versions
• The output of openstack command with -f value has been changed.

On RHOSP13

$ openstack volume list -c "Attached to" --name test-vol1
+----------------------------------------+
| Attached to                            |
+----------------------------------------+
| Attached to test_instance1 on /dev/vda |
+----------------------------------------+

On RHOSP16

$ openstack volume list -f value -c "Attached to" --name test_vol1
[{'id': '<UUID>', 'attachment_id': '<UUID>', 'volume_id': '<UUID>', 'server_id': '<UUID>', 'host_name': 'host1.example.com', 'device': '/dev/vda', 'attached_at': '2020-10-10T10:10:10.000000'}]