Adding (v)host configurable for STOMP protocol

[rob-c]

I found I had to configure the vhost of the STOMP connection in order to connect to a RabbitMQ server at Edinburgh.

I don't know if it's common/best-practice to have a vhost which is the IP of the host associated with the MQ (this is the default from the go library) but I'm aware of a few use-cases where this has not been the case in a setup, hence I've made it configurable.

I've just added a host parameter to the config so that it's picked up and passed onto RabbitMQ correctly. I think this is probably best as a string, but I can't think of a sensible default to add here other than the rabbitmq one of '/' if it's worth making this an optional config parameter.

Happy to change this to 'vhost' rather than 'host' if having this and a url might cause some confusion.

[djw8605]

Yes, I think changing it to vhost to be more explicit is good. I also noticed it's not in the example configuration, could you put it in the example config.