added documentation to support vm_net_ip
added blurb for internal_ip
clarified each interface definition, it's purpose, and clarified variable names between
core.pp and site.pp.example
added tunnel_ip and internal_ip definitions
fixed description for setting $internal_ip and $tunnel_ip
replaced $controller_node_address with $controller_node_internal
for controller creation
Merge pull request #48 from dontalton/multi-node

clarified interface definitions (tunnel_ip, internal_ip), variable names, between core.pp and site.pp