[maven-release-plugin] copy for tag v4.0.0.RC2

Favor DefaultConsumer over QueueingConsumer

Add Nexus staging plugin in appropriate profile

Reduce method visibiliy

References rabbitmq#208

Check outstanding RPC is not null

Before it receives the handling of the command.
The outstanding RPC can be null in case of async call.

Fix TTL test

Merge branch 'rabbitmq-java-client-104' into stable