database/idle_timeout deprecated

The option idle_timeout in the database section is no longer supported in queens.

This is applicable to glance-api and glance-registry. Both have in the logs something like:

2018-12-05 07:58:58.922 53806 WARNING oslo_config.cfg [req-3df6830e-164d-4f00-910b-325dea9b1fa0 678c11b13859448a8a43c8f9412c759d 21c00bd8706242f491cdd1708864231c - default default] Option "idle_timeout" from group "database" is deprecated. Use option "connection_recycle_time" from group "database".

It would also be desirable to be able to tune this parameter (since we can already tune wait-timeout in the mysql charm). But that would be a separate feature request.