Use pickle by default for serialization (#5978)

python/ray/scripts/scripts.py

@@ -233,9 +233,9 @@ def cli(logging_level, logging_format):
     default=False,
     help="Specify whether load code from local file or GCS serialization.")
 @click.option(
-    "--use-pickle",
+    "--use-pickle/--no-use-pickle",
     is_flag=True,
-    default=False,
+    default=ray.cloudpickle.FAST_CLOUDPICKLE_USED,
     help="Use pickle for serialization.")
 def start(node_ip_address, redis_address, address, redis_port,
           num_redis_shards, redis_max_clients, redis_password,