Cinder snapshot delete doesn't end the snapshot resource

Issue

• cinder snapshot resource is not getting ended when the snapshot is deleted.

• What we see is, ceilometer notification is sending it to end, but gnocchi is not performing the action

• Steps to reproduce and ceilometer logs

$ openstack volume snapshot create --volume 3171a35b-e197-4487-a059-7a282040b34c venktestsnap1
+-------------+--------------------------------------+
| Field       | Value                                |
+-------------+--------------------------------------+
| created_at  | 2021-05-14T10:06:22.552005           |
| description | None                                 |
| id          | 18cfefbf-7efb-410b-b462-ec80c88323bd |
| name        | venktestsnap1                        |
| properties  |                                      |
| size        | 1                                    |
| status      | creating                             |
| updated_at  | None                                 |
| volume_id   | 3171a35b-e197-4487-a059-7a282040b34c |

$ om resource show 18cfefbf-7efb-410b-b462-ec80c88323bd
+-----------------------+-------------------------------------------------------------------+
| Field                 | Value                                                             |
+-----------------------+-------------------------------------------------------------------+
| created_by_project_id | 7cdbbd21dd1042779d174e7abf414c12                                  |
| created_by_user_id    | 044a308324234a93a1d12165697b228b                                  |
| creator               | 044a308324234a93a1d12165697b228b:7cdbbd21dd1042779d174e7abf414c12 |
| ended_at              | None                                                              |
| id                    | 18cfefbf-7efb-410b-b462-ec80c88323bd                              |
| metrics               | snapshot.size: 7b24c213-9e11-4796-ab5e-fe2349b21766               |
| original_resource_id  | 18cfefbf-7efb-410b-b462-ec80c88323bd                              |
| project_id            | 33a1e61548e94695be6589fe281dae5c                                  |
| revision_end          | None                                                              |
| revision_start        | 2021-05-14T10:06:22.722093+00:00                                  |
| started_at            | 2021-05-14T10:06:22.722036+00:00                                  |
| type                  | snapshot                                                          |
| user_id               | bfb1d2c70a7d4d948ec4fd7a0a0a2fdc                                  |

$ openstack volume snapshot delete 18cfefbf-7efb-410b-b462-ec80c88323bd

$ om resource show 18cfefbf-7efb-410b-b462-ec80c88323bd
+-----------------------+-------------------------------------------------------------------+
| Field                 | Value                                                             |
+-----------------------+-------------------------------------------------------------------+
| created_by_project_id | 7cdbbd21dd1042779d174e7abf414c12                                  |
| created_by_user_id    | 044a308324234a93a1d12165697b228b                                  |
| creator               | 044a308324234a93a1d12165697b228b:7cdbbd21dd1042779d174e7abf414c12 |
| ended_at              | None                                                              |
| id                    | 18cfefbf-7efb-410b-b462-ec80c88323bd                              |
| metrics               | snapshot.size: 7b24c213-9e11-4796-ab5e-fe2349b21766               |
| original_resource_id  | 18cfefbf-7efb-410b-b462-ec80c88323bd                              |
| project_id            | 33a1e61548e94695be6589fe281dae5c                                  |
| revision_end          | None                                                              |
| revision_start        | 2021-05-14T10:06:22.722093+00:00                                  |
| started_at            | 2021-05-14T10:06:22.722036+00:00                                  |
| type                  | snapshot                                                          |
| user_id               | bfb1d2c70a7d4d948ec4fd7a0a0a2fdc                                  |

• ceilometer logs:

[root@overcloud-ctl01 ceilometer]# grep 18cfefbf-7efb-410b-b462-ec80c88323bd *
agent-notification.log:2021-05-14 10:06:22.730 43 DEBUG ceilometer.publisher.gnocchi [-] Resource 18cfefbf-7efb-410b-b462-ec80c88323bd created _create_resource /usr/lib/python3.6/site-packages/ceilometer/publisher/gnocchi.py:448
agent-notification.log:2021-05-14 10:06:22.797 43 DEBUG ceilometer.publisher.gnocchi [-] Resource 18cfefbf-7efb-410b-b462-ec80c88323bd updated _update_resource /usr/lib/python3.6/site-packages/ceilometer/publisher/gnocchi.py:452
agent-notification.log:2021-05-14 10:06:23.433 43 DEBUG ceilometer.publisher.gnocchi [-] Resource 18cfefbf-7efb-410b-b462-ec80c88323bd updated _update_resource /usr/lib/python3.6/site-packages/ceilometer/publisher/gnocchi.py:452
agent-notification.log:2021-05-14 10:08:39.743 43 DEBUG ceilometer.publisher.gnocchi [-] Resource 18cfefbf-7efb-410b-b462-ec80c88323bd updated _update_resource /usr/lib/python3.6/site-packages/ceilometer/publisher/gnocchi.py:452
agent-notification.log:2021-05-14 10:08:51.286 43 DEBUG ceilometer.publisher.gnocchi [-] Delete event received on unexisting resource (18cfefbf-7efb-410b-b462-ec80c88323bd), ignore it. _set_ended_at /usr/lib/python3.6/site-packages/ceilometer/publisher/gnocchi.py:575
agent-notification.log:2021-05-14 10:08:51.287 43 DEBUG ceilometer.publisher.gnocchi [-] Resource 18cfefbf-7efb-410b-b462-ec80c88323bd ended at 2021-05-14T10:08:50.997434 _set_ended_at /usr/lib/python3.6/site-packages/ceilometer/publisher/gnocchi.py:579
agent-notification.log:2021-05-14 10:08:51.342 43 DEBUG ceilometer.publisher.gnocchi [-] Resource 18cfefbf-7efb-410b-b462-ec80c88323bd updated _update_resource /usr/lib/python3.6/site-packages/ceilometer/publisher/gnocchi.py:452