[Autoscaler] Prefix (autoscaler) instead of (scheduler) for autoscale…

…r events (#31489)

Signed-off-by: praveeng <praveeng@anyscale.com>

# Why are these changes needed?

Autoscaler event logs are prefixed with (scheduler) which is misleading. This PR changes the prefix to be (autoscaler)

Tested building ray locally and running an application (see attached logs). Added unit tests.

# Related issue number

Closes #24807

python/ray/_private/worker.py

@@ -1777,7 +1777,7 @@ def color_for(data: Dict[str, str], line: str) -> str:
             return colorama.Fore.CYAN
 
     if data.get("pid") == "autoscaler":
-        pid = "scheduler +{}".format(time_string())
+        pid = "autoscaler +{}".format(time_string())
         lines = filter_autoscaler_events(data.get("lines", []))
     else:
         pid = data.get("pid")

python/ray/tests/test_output.py

@@ -177,6 +177,30 @@ def f():
     assert "Tip:" not in err_str
 
 
+def test_autoscaler_prefix():
+    script = """
+import ray
+import time
+
+ray.init(num_cpus=1)
+
+@ray.remote(num_cpus=1)
+class A:
+    pass
+
+a = A.remote()
+b = A.remote()
+time.sleep(25)
+    """
+
+    proc = run_string_as_driver_nonblocking(script)
+    out_str = proc.stdout.read().decode("ascii")
+    err_str = proc.stderr.read().decode("ascii")
+
+    print(out_str, err_str)
+    assert "(autoscaler" in out_str
+
+
 @pytest.mark.skipif(sys.platform == "win32", reason="Failing on Windows.")
 def test_fail_importing_actor(ray_start_regular, error_pubsub):
     script = f"""