<issue_start><issue_comment>Title: RFE: Add possibility to add cleanup events (from postgresql)
username_0: The test for the PostgreSQL container includes a nice function `add_cleanup_command` that allows to extend the default `cleanup` action. It would be good to have this function in the `test-lib.sh` so we can use it in other container images tests as well:
https://github.com/sclorg/postgresql-container/blob/1cbbb075/test/run_test#L48-L58