Fix LRU eviction of client notification datastructure (#4021)

* convert notification_key map to C++ datastructure

* fix crash and add debug string

* clean notification map up (this was a bug before)

* remove checks

* add jenkins test

* linting

* fixes

* properly erase

* clean up

* linting

* Update test_wait_hanging.py

* Update run_multi_node_tests.sh

* increase redis_max_memory

* fix dat jenkins

* update

* Update run_multi_node_tests.sh

test/jenkins_tests/multi_node_tests/test_wait_hanging.py

@@ -0,0 +1,31 @@
+from __future__ import absolute_import
+from __future__ import division
+from __future__ import print_function
+
+import ray
+
+
+@ray.remote
+def f():
+    return 0
+
+
+@ray.remote
+def g():
+    import time
+    start = time.time()
+    while time.time() < start + 1:
+        ray.get([f.remote() for _ in range(10)])
+
+
+# 10MB -> hangs after ~5 iterations
+# 20MB -> hangs after ~20 iterations
+# 50MB -> hangs after ~50 iterations
+ray.init(redis_max_memory=1024 * 1024 * 50)
+
+i = 0
+for i in range(100):
+    i += 1
+    a = g.remote()
+    [ok], _ = ray.wait([a])
+    print("iter", i)