Migration of legacy XML format command always uses the default database, then command cannot migrate data from other DB from a repository siteaccess.

steps to reproduce
1. Create a fresh installation of eZ Platform.
2. Configure two DB connections and repositories to uses two different DB.
3. Fill database to migration
4. Run ezplatform:migrate:legacy_matrix command with siteaccess parameter to non-default DB connection

Result:
Command use default DB 

Expected result:
Command will use a valid database