Disable pipelined write in atomic flush stress test (#5266)

Summary:
Since currently pipelined write allows one thread to perform memtable writes
while another thread is traversing the `flush_scheduler_`, it will cause an
assertion failure in `FlushScheduler::Clear`. To unblock crash recoery tests,
we temporarily disable pipelined write when atomic flush is enabled.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5266

Differential Revision: D15142285

Pulled By: riversand963

fbshipit-source-id: a0c20fe4ac543e08feaed602414f982054df7831

tools/db_crashtest.py

@@ -136,6 +136,8 @@ atomic_flush_params = {
     # use small value for write_buffer_size so that RocksDB triggers flush
     # more frequently
     "write_buffer_size": 1024 * 1024,
+    # disable pipelined write when test_atomic_flush is true
+    "enable_pipelined_write": 0,
 }