Fix webui api (#4686)

* fix webui

* Apply suggestions from code review

lint

Co-Authored-By: suquark <suquark@gmail.com>

* add dependencies for this unittest

* move dependencies to the script file

python/ray/tests/test_webui.py

@@ -0,0 +1,17 @@
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import sys
+import pytest
+import ray
+
+
+@pytest.mark.skipif(
+    sys.version_info < (3, 5, 3), reason="requires python3.5.3 or higher")
+def test_get_webui():
+    addresses = ray.init(include_webui=True)
+    webui_url = addresses["webui_url"]
+    assert ray.worker.get_webui_url() == webui_url
+
+    ray.shutdown()