Summary:
Add crash test for the case of best-efforts recovery.
After a certain amount of time, we kill the db_stress process, randomly delete some certain table files and restart db_stress. Given the randomness of file deletion, it is difficult to verify against a reference for data correctness. Therefore, we just check that the db can restart successfully.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/6819
Test Plan:
```
./db_stress -best_efforts_recovery=true -disable_wal=1 -reopen=0
./db_stress -best_efforts_recovery=true -disable_wal=0 -skip_verifydb=1 -verify_db_one_in=0 -continuous_verification_interval=0
make crash_test_with_best_efforts_recovery
```
Reviewed By: anand1976
Differential Revision: D21436753
Pulled By: riversand963
fbshipit-source-id: 0b3605c922a16c37ed17d5ab6682ca4240e47926
15d9f28da5