DRILL-2782: 2-Core: Decide, implement behavior for transaction-related JDBC methods.
- Added unit test.
- Added implementations of transaction-related methods:
- setAutoCommit - reject attempt to turn auto-commit off
- commit - reject when in auto-commit mode (which is always)
- rollback - reject when in auto-commit mode (which is always)
- other mode and metadata methods - roughly, report "no transactions"
- Added method declarations with doc. comments in Drill-specific interface.
- Overrode SQLLine's default transaction isolation level to Drill's
TRANSACTION_NONE.
