Update quorum on deletion

If deletion of a node brings quorum, notify followers
of the good news

confluent_server/confluent/config/configmanager.py

@@ -1013,6 +1013,14 @@ def del_collective_member(name):
     if cfgstreams:
         exec_on_followers_unconditional('_true_del_collective_member', name)
     _true_del_collective_member(name)
+    if cfgstreams:
+        _hasquorum = has_quorum()
+        pushes = eventlet.GreenPool()
+        payload = msgpack.packb({'quorum': _hasquorum}, use_bin_type=False)
+        for _ in pushes.starmap(
+                _push_rpc,
+                [(cfgstreams[s]['stream'], payload) for s in cfgstreams]):
+            pass
 
 def _true_del_collective_member(name, sync=True):
     global cfgleader