Pools are not properly updated by MySQL CB when subnet id is modified

MySQL CB allows for modifying subnet id with remote-subnet4-set and remote-subnet6-set. However, there is a bug in MySQL logic, which causes duplication of the pool during such update. Prior to updating the subnet information, the backend deletes existing pools. Then it recreates them after the subnet is updated. The backend mistakenly uses new subnet id for deleting the pools. As a result the pools remain in the database. Recreating the pools causes duplication of the pool entry and failure to merge the configuration into the server's configuration.