nova-api logs are spammed with oslo.messaging errors

Issue

• missed heartbeats from client, timeout errors in RabbitMQ logs:

  2019-04-15 16:31:25.760 [error] <0.3565.0> closing AMQP connection <0.3565.0> (10.109.1.2:33356 -> 10.109.1.2:5672 - mod_wsgi:20:f78bdc50-0734-4823-b91b-7c9ac4227fd0): missed heartbeats from client, timeout: 60s
  

• OSError: Server unexpectedly closed connection errors in nova-api logs, other OpenStack services are not affected

  nova/nova-api.log:2019-04-15 16:30:27.358 19 WARNING oslo.messaging._drivers.impl_rabbit [-] Unexpected error during heartbeart thread processing, retrying...: OSError: Server unexpectedly closed connection