Don't use user with DBA permissions for Oracle connector tests

The tests are currently done using the xstrmadmin user which as DBA permissions. Instead, the following should be done:

• the xstrmadmin user shouldn't need DBA permissions, as it's a dedicated admin for the XStream artifacts
• the connector shouldn't connect using the xstrmadmin user but a separate account, which is neither a system DBA nor an XStream admin