AMSlib: rabbitmq-exchange fields cannot be empty

[lpottier]

If the field rabbitmq-exchange is empty AMSlib raises an error (no matter the value of update_surrogate).

{
  {
    "rabbitmq-outbound-queue": "",
    "rabbitmq-exchange": "",
    "rabbitmq-routing-key": ""
  },
  "update_surrogate": false
}

This behavior should be modified to not start an RMQConsumer if update_surrogate is false. If update_surrogate is true and rabbitmq-exchange is empty then we should raise an error.

In addition the fields rabbitmq-outbound-queue, rabbitmq-exchange, rabbitmq-routing-key should be renamed to be more expressive.