Nova create duplicate cells when templates are used

Also attaching how database looks like after several runs of the command:

MariaDB [nova_api]> select * from cell_mappings;
+---------------------+---------------------+----+--------------------------------------+-------+-------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------+----------+
| created_at | updated_at | id | uuid | name | transport_url | database_connection | disabled |
+---------------------+---------------------+----+--------------------------------------+-------+-------------------------------------------------------------+-----------------------------------------------------------------------------------------------------------------------------+----------+
| 2021-04-14 10:49:46 | NULL | 1 | 00000000-0000-0000-0000-000000000000 | cell0 | none:/// | mysql+pymysql://nova_api:e83ceeb01f3093de3f23de63c4a9d229eb78ce49a15acfb1894b754397d@172.29.236.101/nova_cell0?charset=utf8 | 0 |
| 2021-04-14 10:50:17 | 2021-04-14 14:54:24 | 2 | ef89aebc-142d-4755-a377-6ed23b6c1ed4 | cell1 | {scheme}://{username}:{password}@{hostname}//{path}?{query} | {scheme}://{username}:{password}@{hostname}/{path}?{query} | 0 |
| 2021-04-14 19:39:33 | NULL | 4 | e22e06d5-b668-47a6-943c-169c2ed976a4 | cell1 | {scheme}://{username}:{password}@{hostname}//{path}?{query} | {scheme}://{username}:{password}@{hostname}/{path}?{query} | 0 |
| 2021-04-14 19:39:40 | NULL | 5 | 8be204c1-0710-4b0a-a1c5-9a42707bbaa7 | cell1 | {scheme}://{username}:{password}@{hostname}//{path}?{query} | {scheme}://{username}:{password}@{hostname}/{path}?{query} | 0 |
| 2021-04-14 19:39:49 | NULL | 6 | f34f0e6c-98e8-4da6-91c5-46d0234afd0e | cell1 | {scheme}://{username}:{password}@{hostname}//{path}?{query} | {scheme}://{username}:{password}@{hostname}/{path}?{query} | 0 |
| 2021-04-14 19:41:50 | NULL | 7 | 046c88f0-097e-4a7c-9eee-45654355ff56 | cell1 | {scheme}://{username}:{password}@{hostname}//{path}?{query} | {scheme}://{username}:{password}@{hostname}/{path}?{query} | 0 |
| 2021-04-14 19:41:54 | NULL | 8 | b5f1672e-36c7-4d17-90b3-7433842cbbe0 | cell1 | {scheme}://{username}:{password}@{hostname}//{path}?{query} | {scheme}://{username}:{password}@{hostname}/{path}?{query} | 0 |
| 2021-04-14 19:41:58 | NULL | 9 | cf2efc1c-e091-4c93-96d4-84b3ecfa4647 | cell1 | {scheme}...

Looking at the code I confirm that it is a bug.

Fix proposed to branch: master
Review: https://review.opendev.org/c/openstack/nova/+/876940