Ensure ATs are covering the proper databases/drivers

[onobc]

Now that we support MySQL5/8+ and Maria 10.4+ via the Maria 3.x driver, we need. to make sure that our DB ATs are exercising the proper permutations.

[onobc]

Rather than invest time in shoehorning MySQL support in the DB ITs we are going to instead move these ITs into the ATs as @corneil has added the ability to easily specify DB combinations.

We currently have coverage for MySQL 5.7, MariaDB, Postgres in the ATs and will be adding more support as we go. We do not want to debug/maintain the same tests in multiple places.