verify the replyTo queue still exists before running the command

[jfromaniello]

Add a parameter to verify if the replyTo queue still exists before running the command.

I took this idea from rabbitmq documentation:

If the RPC server is going to perform some expensive computation it might wish to check if the client has gone away. To do this the server can declare the generated reply name first on a disposable channel in order to determine whether it still exists.