Summary:
**Context:**
`BackupEngineRateLimitingTestWithParam.RateLimiting` and `BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup` involve creating backup and restoring of a big database with rate-limiting. Using the normal env with a normal clock requires real elapse of time (13702 - 19848 ms/per test). As suggested in https://github.com/facebook/rocksdb/pull/8722#discussion_r703698603, this PR is to speed it up with SpecialEnv (`time_elapse_only_sleep=true`) where its clock accepts fake elapse of time during rate-limiting (100 - 600 ms/per test)
**Summary:**
- Added TEST_ function to set clock of the default rate limiters in backup engine
- Shrunk testdb by 10 times while keeping it big enough for testing
- Renamed some test variables and reorganized some if-else branch for clarity without changing the test
Pull Request resolved: https://github.com/facebook/rocksdb/pull/9974
Test Plan:
- Run tests pre/post PR the same time to verify the tests are sped up by 90 - 95%
`BackupEngineRateLimitingTestWithParam.RateLimiting`
Pre:
```
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/0
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/0 (11123 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/1
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/1 (9441 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/2
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/2 (11096 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/3
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/3 (9339 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/4
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/4 (11121 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/5
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/5 (9413 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/6
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/6 (11185 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/7
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/7 (9511 ms)
[----------] 8 tests from RateLimiting/BackupEngineRateLimitingTestWithParam (82230 ms total)
```
Post:
```
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/0
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/0 (395 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/1
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/1 (564 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/2
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/2 (358 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/3
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/3 (567 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/4
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/4 (173 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/5
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/5 (176 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/6
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/6 (191 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/7
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimiting/7 (177 ms)
[----------] 8 tests from RateLimiting/BackupEngineRateLimitingTestWithParam (2601 ms total)
```
`BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup`
Pre:
```
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/0
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/0 (7275 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/1
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/1 (3961 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/2
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/2 (7117 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/3
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/3 (3921 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/4
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/4 (19862 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/5
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/5 (10231 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/6
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/6 (19848 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/7
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/7 (10372 ms)
[----------] 8 tests from RateLimiting/BackupEngineRateLimitingTestWithParam (82587 ms total)
```
Post:
```
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/0
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/0 (157 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/1
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/1 (152 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/2
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/2 (160 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/3
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/3 (158 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/4
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/4 (155 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/5
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/5 (151 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/6
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/6 (146 ms)
[ RUN ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/7
[ OK ] RateLimiting/BackupEngineRateLimitingTestWithParam.RateLimitingVerifyBackup/7 (153 ms)
[----------] 8 tests from RateLimiting/BackupEngineRateLimitingTestWithParam (1232 ms total)
```
Reviewed By: pdillinger
Differential Revision: D36336345
Pulled By: hx235
fbshipit-source-id: 724c6ba745f95f56d4440a6d2f1e4512a2987589
e66e6d2faa