Major Description
Background discussion in KAFKA-320
People often try to embed KafkaServer in an application that ends up calling startup() and shutdown() repeatedly and sometimes in odd ways. To ensure this works correctly we have to be very careful about cleaning up resources. This is a good practice for making unit tests reliable anyway.
A good first step would be to add some unit tests on startup and shutdown to cover various cases:
1. A Kafka server can startup if it is not already starting up, if it is not currently being shutdown, or if it hasn't been already started
2. A Kafka server can shutdown if it is not already shutting down, if it is not currently starting up, or if it hasn't been already shutdown.