[xray] Adds a driver table. (#2289)

This PR adds a driver table for the new GCS, which enables cleanup functionality associated with monitoring driver death.

Some testing in `monitor_test.py` is restored, but redis sharding for xray is needed to enable remaining tests.

src/common/lib/python/common_extension.cc

@@ -907,3 +907,12 @@ PyObject *check_simple_value(PyObject *self, PyObject *args) {
   }
   Py_RETURN_FALSE;
 }
+
+PyObject *compute_task_id(PyObject *self, PyObject *args) {
+  ObjectID object_id;
+  if (!PyArg_ParseTuple(args, "O&", &PyObjectToUniqueID, &object_id)) {
+    return NULL;
+  }
+  TaskID task_id = ray::ComputeTaskId(object_id);
+  return PyObjectID_make(task_id);
+}

src/common/lib/python/common_extension.h

@@ -56,6 +56,7 @@ int PyObjectToUniqueID(PyObject *object, ray::ObjectID *object_id);
 PyObject *PyObjectID_make(ray::ObjectID object_id);
 
 PyObject *check_simple_value(PyObject *self, PyObject *args);
+PyObject *compute_task_id(PyObject *self, PyObject *args);
 
 PyObject *PyTask_to_string(PyObject *, PyObject *args);
 PyObject *PyTask_from_string(PyObject *, PyObject *args);