DRILL-2887: Fix bad applications of JdbcTest.connect(...).
- Removed use of Jdbc.connect() from:
- Drill2128GetColumnsDataTypeNotTypeCodeIntBugsTest
- Drill2489CallsAfterCloseThrowExceptionsTest
- Added (manual) test for use of auto-resetting connection. [JdbcTest]
- Documented need to avoid Jdbc.connect() in above and similar tests.
- Add "document" TODO for JdbcTest.
