DRILL-4880: Support JDBC driver registration using ServiceLoader
Support loading Drill driver using ServiceLoader. From the user perspective,
it means being able to use the driver without registering it first, like by using
Class.forName("org.apache.drill.jdbc.Driver") for example.
this closes #596
Change-Id: Id26922ee42bef5fbce46ac2bcbb83f1859e9bb48
