[launch] Support IPv4 host initialization in launch (#5822)

colossalai/initialize.py

@@ -45,7 +45,10 @@ def launch(
     backend = cur_accelerator.communication_backend
 
     # init default process group
-    init_method = f"tcp://[{host}]:{port}"
+    if ":" in host:  # IPv6
+        init_method = f"tcp://[{host}]:{port}"
+    else:  # IPv4
+        init_method = f"tcp://{host}:{port}"
     dist.init_process_group(rank=rank, world_size=world_size, backend=backend, init_method=init_method)
 
     # set cuda device