Improve code related to node (#4383)

* Make full use of node

implement local node

fix bugs mentioned in comments

* Add more tests

* Use more specific exception handling

* fix, lint

* fix for py2.x

python/ray/tests/test_tempfile.py

@@ -7,6 +7,13 @@ import shutil
 import time
 import pytest
 import ray
+from ray.tests.cluster_utils import Cluster
+
+# Py2 compatibility
+try:
+    FileNotFoundError
+except NameError:
+    FileNotFoundError = OSError
 
 
 def test_conn_cluster():
@@ -52,8 +59,17 @@ def test_raylet_socket_name():
     ray.shutdown()
     try:
         os.remove("/tmp/i_am_a_temp_socket")
-    except Exception:
-        pass
+    except FileNotFoundError:
+        pass  # It could have been removed by Ray.
+    cluster = Cluster(True)
+    cluster.add_node(raylet_socket_name="/tmp/i_am_a_temp_socket_2")
+    assert os.path.exists(
+        "/tmp/i_am_a_temp_socket_2"), "Specified socket path not found."
+    cluster.shutdown()
+    try:
+        os.remove("/tmp/i_am_a_temp_socket_2")
+    except FileNotFoundError:
+        pass  # It could have been removed by Ray.
 
 
 def test_temp_plasma_store_socket():
@@ -63,8 +79,17 @@ def test_temp_plasma_store_socket():
     ray.shutdown()
     try:
         os.remove("/tmp/i_am_a_temp_socket")
-    except Exception:
-        pass
+    except FileNotFoundError:
+        pass  # It could have been removed by Ray.
+    cluster = Cluster(True)
+    cluster.add_node(plasma_store_socket_name="/tmp/i_am_a_temp_socket_2")
+    assert os.path.exists(
+        "/tmp/i_am_a_temp_socket_2"), "Specified socket path not found."
+    cluster.shutdown()
+    try:
+        os.remove("/tmp/i_am_a_temp_socket_2")
+    except FileNotFoundError:
+        pass  # It could have been removed by Ray.
 
 
 def test_raylet_tempfiles():