fix: use unique AMQP username for NovaComputeNode

Add uid of the NovaCompute as suffix to the RabbitMQ username inside the AMQPUser to use a unique username after each recreation of the AMQPUser (which is done with the recreation of a NovaComputeNode). This prevents the current nova-compute user from being deleted inside RabbitMQ if an error occurs during a previous reconciliation of the old AMQPUser instance and Yaook later deletes the old AMQPUser while the new AMQPUser already exists. In that case, communication between the nova-compute pod is not possible until the new AMQPUser is reconciled again, leading to volumes stuck in attaching and other undesirable outcomes. After this change is rolled out, existing AMQPUsers will not be changed and the uid suffix will only affect recreated AMQPUsers.

Plus: Verify that there are no duplicate AMQPUsers inside integration test.