DBAL-492: Foreign keys always changed with postgres non standard schema.

Jira issue originally created by user fleetfox:

Starting with this https://github.com/doctrine/dbal/commit/b84cda24335207d4e60afc88fa161317d94b6370#diff-0 all foreign keys in non standard schema all always different, because table1 doesn't contain a schema name in it but table2 does.
