Add user configurable gateway name to VM setup

[ccustine]

We are going to need a simple way to template the configs for Kura so that the user can set the gateway name. This affects the way that Kura publishes to MQTT topics, and currently all VMs created publish to the same topic structure. This causes any clients to get multiple data streams that overlap when run simultaneously with another user.

Another option would be to use the currently logged in userid, but either way will require templating the configs.