rgsandbox as a submodule and no more private network

* rgsandbox added as submodule (so it is already mounted in the Vagrant VM and can be used)
* removed (IMO) unnecessary virtual adapter creation (Vagrant private network) and instead configured a port-forward from/to port 8080, with collision resolution, only available on localhost on the host machine.
Use `guest: 80` instead so it matches nginx port.