The tests are using the local object storage configured in the docker
compose stack. Every time a test using the DocumentFactory is executed,
an object is created in the object storage and will stay here but never
used. The data/media directory is growing and time to time we have to
delete it in order to free some gigabytes. In this commit we add a
global conftest responsible to delete the object created during the test
execution. The space will be really free when the object storage
container will be shutdown.