Running the testsuite against a PostgreSQL DB issues many errors.
While tests are marked to be skipped, the call to parent::setUp() generates errors.

In a general way, we should skip tests before the call to parent::setUp() is made unless skipping can only be figured depending on the parent::setUp() call.

Steps to reproduce

php tests/runtests.php --db-per-test --dsn postgresql://...@localhost/ezpublish -f eZDFSFileHandlerTest