Summary:
- Attempt to clean the checkpoint staging directory before starting a checkpoint. It was already cleaned up at the end of checkpoint. But it wasn't cleaned up in the edge case where the process crashed while staging checkpoint files.
- Attempt to clean the checkpoint directory before calling `Checkpoint::Create` in `db_stress`. This handles the case where checkpoint directory was created by a previous `db_stress` run but the process crashed before cleaning it up.
- Use `DestroyDB` for cleaning checkpoint directory since a checkpoint is a DB.
Closes https://github.com/facebook/rocksdb/pull/4035
Reviewed By: yiwu-arbug
Differential Revision: D8580223
Pulled By: ajkr
fbshipit-source-id: 28c667400e249fad0fdedc664b349031b7b61599
0a5b16c7c5