Correct database deployment yaml file

[m-czernek]

On OpenShift 4.4, the database deployment fails with the following error:

020-07-28 17:37:03+00:00 [Note] [Entrypoint]: Entrypoint script for MySQL Server 5.7.31-1debian10 started.
2020-07-28 17:37:03+00:00 [Note] [Entrypoint]: Initializing database files
mysqld: Can't create/write to file '/var/lib/mysql/is_writable' (Errcode: 13 - Permission denied)
2020-07-28T17:37:03.256943Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
2020-07-28T17:37:03.258135Z 0 [ERROR] --initialize specified but the data directory exists and is not writable. Aborting.
2020-07-28T17:37:03.258149Z 0 [ERROR] Aborting

This change fixes the error and makes deployment possible (while keeping the mount ephemeral).