Summary:
thread_id is only unique within a process. If we run the same test-set with multiple processes, it could cause db path collision between 2 runs, error message will be like:
```
...
IO error: While lock file: /tmp/rocksdbtest-501//deletefile_test_8093137327721791717/LOCK: Resource temporarily unavailable
...
```
This is could be likely reproduced by:
```
gtest-parallel ./deletefile_test --gtest_filter=DeleteFileTest.BackgroundPurgeCFDropTest -r 1000 -w 1000
```

Pull Request resolved: https://github.com/facebook/rocksdb/pull/8124

Reviewed By: ajkr

Differential Revision: D27435195

Pulled By: jay-zhuang

fbshipit-source-id: 850fc72cdb660edf93be9a1ca9327008c16dd720