rabbitmq: don't wait for message ack/requeue

I don't see any obvious reason why we should wait ack/requeue is done.

This waiter have already be removed from amqp1.

https://git.openstack.org/cgit/openstack/oslo.messaging/tree/oslo_messaging/_drivers/amqp1_driver/controller.py#n242

So, this change remove it from rabbitmq driver too.

Closes-bug: #1734788

Change-Id: I5ecedc762596181be19410b863851a0054fd6579
(cherry picked from commit c38857e110)

oslo_messaging/_drivers/amqpdriver.py

@@ -82,26 +82,14 @@ class MessageOperationsHandler(object):
 
         while True:
             try:
-                task, event = self._tasks.get(block=False)
+                task = self._tasks.get(block=False)
             except moves.queue.Empty:
                 break
-            try:
-                task()
-            finally:
-                event.set()
+            task()
 
     def do(self, task):
-        "Put the task in the queue and waits until the task is completed."
-        if self._executor is None:
-            raise RuntimeError("Unexpected error, no executor is setuped")
-        elif self._executor == "blocking":
-            # NOTE(sileht): Blocking will hang forever if we waiting the
-            # polling thread
-            task()
-        else:
-            event = threading.Event()
-            self._tasks.put((task, event))
-            event.wait()
+        "Put the task in the queue."
+        self._tasks.put(task)
 
 
 class AMQPIncomingMessage(base.RpcIncomingMessage):

releasenotes/notes/rabbit-no-wait-for-ack-9e5de3e1320d7660.yaml

@@ -0,0 +1,12 @@
+---
+other:
+  - |
+    On rabbitmq, in the past, acknownlegement of messages was done within the
+    application callback thread/greenlet. This thread was blocked until the
+    message was ack. In newton, we rewrote the message acknownlegement to
+    ensure we haven't two threads writting the the socket at the same times.
+    Now all pendings ack are done by the main thread. They are no more reason
+    to block the application callback thread until the message is ack. Other
+    driver already release the application callback threads before the message
+    is acknownleged. This is also the case for rabbitmq, now.
+