Add virtual host support for amqp:// generation.

[nickb937]

IAmqpCacoonConfig requires a optional field to specify the virtual host and getFullHostName() just needs to add the virtual host onto the URL, if it is defined. After doing that, RabbitMQ users that are defined with access to a virtual host other than '/' will be able to connect.

It is possible to connect by building a IAmqpCacoonConfig.connectionString instead.