Fix scheduler listener on buster's celery version (4.1.0-4)

Without this, the listener just fails as some internal function is no longer defined:

• Problem 1.

Traceback (most recent call last):
  File "/usr/lib/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/tony/work/inria/repo/swh/swh-environment/swh-scheduler/swh/scheduler/celery_backend/listener.py", line 178, in <module>
    main()
  File "/usr/lib/python3/dist-packages/click/core.py", line 722, in __call__
    return self.main(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/click/core.py", line 697, in main
    rv = self.invoke(ctx)
  File "/usr/lib/python3/dist-packages/click/core.py", line 895, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/lib/python3/dist-packages/click/core.py", line 535, in invoke
    return callback(*args, **kwargs)
  File "/home/tony/work/inria/repo/swh/swh-environment/swh-scheduler/swh/scheduler/celery_backend/listener.py", line 174, in main
    event_monitor(main_app, backend=scheduler)
  File "/home/tony/work/inria/repo/swh/swh-environment/swh-scheduler/swh/scheduler/celery_backend/listener.py", line 149, in event_monitor
    node_id='listener-%s' % socket.gethostname(),
  File "/home/tony/work/inria/repo/swh/swh-environment/swh-scheduler/swh/scheduler/celery_backend/listener.py", line 30, in __init__
    queue_arguments=self._get_queue_arguments())
AttributeError: 'ReliableEventReceiver' object has no attribute '_get_queue_arguments'

• Problem 2.

Traceback (most recent call last):
  File "/usr/lib/python3.6/runpy.py", line 193, in _run_module_as_main
    "__main__", mod_spec)
  File "/usr/lib/python3.6/runpy.py", line 85, in _run_code
    exec(code, run_globals)
  File "/home/tony/work/inria/repo/swh/swh-environment/swh-scheduler/swh/scheduler/celery_backend/listener.py", line 207, in <module>
    main()
  File "/usr/lib/python3/dist-packages/click/core.py", line 759, in __call__
    return self.main(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/click/core.py", line 714, in main
    rv = self.invoke(ctx)
  File "/usr/lib/python3/dist-packages/click/core.py", line 951, in invoke
    return ctx.invoke(self.callback, **ctx.params)
  File "/usr/lib/python3/dist-packages/click/core.py", line 552, in invoke
    return callback(*args, **kwargs)
  File "/home/tony/work/inria/repo/swh/swh-environment/swh-scheduler/swh/scheduler/celery_backend/listener.py", line 203, in main
    event_monitor(main_app, backend=scheduler)
  File "/home/tony/work/inria/repo/swh/swh-environment/swh-scheduler/swh/scheduler/celery_backend/listener.py", line 173, in event_monitor
    recv.capture(limit=None, timeout=None, wakeup=True)
  File "/usr/local/lib/python3.6/dist-packages/celery/events/receiver.py", line 92, in capture
    return list(self.consume(limit=limit, timeout=timeout, wakeup=wakeup))
  File "/usr/local/lib/python3.6/dist-packages/kombu/mixins.py", line 192, in consume
    conn.drain_events(timeout=safety_interval)
  File "/usr/local/lib/python3.6/dist-packages/kombu/connection.py", line 301, in drain_events
    return self.transport.drain_events(self.connection, **kwargs)
  File "/usr/local/lib/python3.6/dist-packages/kombu/transport/pyamqp.py", line 103, in drain_events
    return connection.drain_events(**kwargs)
  File "/usr/local/lib/python3.6/dist-packages/amqp/connection.py", line 491, in drain_events
    while not self.blocking_read(timeout):
  File "/usr/local/lib/python3.6/dist-packages/amqp/connection.py", line 497, in blocking_read
    return self.on_inbound_frame(frame)
  File "/usr/local/lib/python3.6/dist-packages/amqp/method_framing.py", line 77, in on_frame
    callback(channel, msg.frame_method, msg.frame_args, msg)
  File "/usr/local/lib/python3.6/dist-packages/amqp/connection.py", line 501, in on_inbound_method
    method_sig, payload, content,
  File "/usr/local/lib/python3.6/dist-packages/amqp/abstract_channel.py", line 128, in dispatch_method
    listener(*args)
  File "/usr/local/lib/python3.6/dist-packages/amqp/channel.py", line 1597, in _on_basic_deliver
    fun(msg)
  File "/usr/local/lib/python3.6/dist-packages/kombu/messaging.py", line 624, in _receive_callback
    return on_m(message) if on_m else self.receive(decoded, message)
  File "/usr/local/lib/python3.6/dist-packages/kombu/messaging.py", line 590, in receive
    [callback(body, message) for callback in callbacks]
  File "/usr/local/lib/python3.6/dist-packages/kombu/messaging.py", line 590, in <listcomp>
    [callback(body, message) for callback in callbacks]
  File "/home/tony/work/inria/repo/swh/swh-environment/swh-scheduler/swh/scheduler/celery_backend/listener.py", line 47, in _receive
    type, body = self.event_from_message(body)
  File "/usr/local/lib/python3.6/dist-packages/celery/events/receiver.py", line 103, in event_from_message
    type = body['type']
TypeError: list indices must be integers or slices, not str

version:

$ dpkg -l python3-celery
Desired=Unknown/Install/Remove/Purge/Hold
| Status=Not/Inst/Conf-files/Unpacked/halF-conf/Half-inst/trig-aWait/Trig-pend
|/ Err?=(none)/Reinst-required (Status,Err: uppercase=bad)
||/ Name                                                           Version                              Architecture                         Description
+++-==============================================================-====================================-====================================-=================================================================================================================================
ii  python3-celery                                                 4.1.0-4                              all                                  async task/job queue based on message passing (Python3 version)

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Migrated from D312 (view on Phabricator)