Checkpoint dir options fix (#8572)

Checkpoint dir options fix (#8572)

Summary:
Originally the 2 options `db_log_dir` and `wal_dir` will be reused in a snapshot db since the options files are just copied. By default, if `wal_dir` was not set when a db was created, it is set to the db's dir. Therefore, the snapshot db will use the same WAL dir. If both the original db and the snapshot db write to or delete from the WAL dir, one may modify or delete files which belong to the other. The same applies to `db_log_dir` as well, but as info log files are not copied or linked, it is simpler for this option.

2 arguments are added to `Checkpoint::CreateCheckpoint()`, allowing to override these 2 options.

`wal_dir`:  If the function argument `wal_dir` is empty, or set to the original db location, or the checkpoint location, the snapshot's `wal_dir` option will be updated to the checkpoint location. Otherwise, the absolute path specified in the argument will be used. During checkpointing, live WAL files will be copied or linked the new location, instead of the current WAL dir specified in the original db.

`db_log_dir`: Same as `wal_dir`, but no files will be copied or linked.

A new unit test was added: `CheckpointTest.CheckpointWithOptionsDirsTest`.

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8572

Test Plan:
New unit test
```
checkpoint_test --gtest_filter="CheckpointTest.CheckpointWithOptionsDirsTest"
```

Output
```
Note: Google Test filter = CheckpointTest.CheckpointWithOptionsDirsTest
[==========] Running 1 test from 1 test case.
[----------] Global test environment set-up.
[----------] 1 test from CheckpointTest
[ RUN      ] CheckpointTest.CheckpointWithOptionsDirsTest
[       OK ] CheckpointTest.CheckpointWithOptionsDirsTest (11712 ms)
[----------] 1 test from CheckpointTest (11712 ms total)

[----------] Global test environment tear-down
[==========] 1 test from 1 test case ran. (11713 ms total)
[  PASSED  ] 1 test.
```
This test will fail without this patch. Just modify the code to remove the 2 arguments introduced in this patch in `CreateCheckpoint()`.

Reviewed By: zhichao-cao

Differential Revision: D29832761

Pulled By: autopear

fbshipit-source-id: e6a639b4d674380df82998c0839e79cab695fe29