Disable MultiGet from db_stress (#5284)

Summary:
Disable it for now until we can get stress tests to pass consistently.
Pull Request resolved: https://github.com/facebook/rocksdb/pull/5284

Differential Revision: D15230727

Pulled By: anand1976

fbshipit-source-id: 239baacdb3c4cd4fb7c4447f7582b9042501d752

tools/db_crashtest.py

@@ -65,7 +65,7 @@ default_params = {
     "writepercent": 35,
     "format_version": lambda: random.randint(2, 4),
     "index_block_restart_interval": lambda: random.choice(range(1, 16)),
-    "use_multiget" : lambda: random.randint(0, 1),
+    "use_multiget" : 0,
 }
 
 _TEST_DIR_ENV_VAR = 'TEST_TMPDIR'