- Fix the LooseScan code to support storage engines that return
  HA_ERR_END_OF_FILE if the index scan goes out of provided range
  bounds
- Add a DBUG_EXECUTE_IF("force_group_by",...) to allow a test to
  force a LooseScan
- Adjust rocksdb.group_min_max test not to use features not present
  in MariaDB 10.2 (e.g. optimizer_trace.  In MariaDB 10.4 it's present
  but it doesn't meet the  assumptions that the test makes about it
- Adjust the test result file:
  = MariaDB doesn't support "Enhanced Loose Scan" that FB/MySQL has
  = MariaDB has different cost calculations.