[DS-2128] Eliminate dspace.cfg:db.name

https://jira.duraspace.org/browse/DS-2128

Most of the changed files merely had their own tests for DBMS brand replaced with asking DatabaseManager, which should encapsulate the details of producing this knowledge.  Most of the interesting stuff is in DatasourceInit and DatabaseManager.

There is the beginning of unit tests for DatabaseManager.

This needs a lot more testing.