Heartbeat not sent for listen connections waiting for a message

When using heartbeat_in_pthreads = True, the threading and queue libraries are not eventlet monkey patched anymore for heartbeats (see [1])

Because of this, when waiting for a message, the queue.get(block=True) (see [2]) completely blocks the thread, preventing it to send heartbeats.

After a while, the connection could be dropped by rabbitmq because of missing heartbeats.

Note that it also depends on rpc_response_timeout value, which, by luck, is 60 sec by default (same as heartbeat timeout), so with default values this bug is not triggered, but if you try to increase rpc_response_timeout to 300secs and stop nova-conductor, you will see some nova-compute RPC connection beeing killed by rabbitmq servers because of misses heartbeats.

[1] https://github.com/openstack/oslo.messaging/blob/7705b4f3023e0e63f3b37e9a25c774f309fec55e/oslo_messaging/_drivers/impl_rabbit.py#L630-L657
[2] https://github.com/openstack/oslo.messaging/blob/7705b4f3023e0e63f3b37e9a25c774f309fec55e/oslo_messaging/_drivers/amqpdriver.py#L441