Fix cleanup of resources for object_storage tests

Some object_storage tests were not cleaning up properly the created
containers.

This patch modifies PublicObjectTest and ObjectACLsNegativeTest tests
so that they clean the created resources properly.

Modification of delete_containers was necessary as well because it
was failing to delete containers with expired objects.

Related-Bug: #1996624
Change-Id: I11ddeb43ce4720f8adfbea5fabfeeb73d7181d68
3 files changed