Support port mappings for VM access instead of subnet

[JesseEstum]

Just curious if anyone would consider or is interested in a configuration whereby the VM running docker engine is accessed through port mapping (e.g., 127.0.0.1:2375) instead of a separate IP on a internal-network subnet (e.g., 192.168.42.2:2375 given the default subnet of 192.168.42.0/24).

A use case for this would be people on corporate VPN connections. Often a VPN client forces all non-whitelisted subnets to be routed through the VPN tunnel - thereby making it impossible to route to a VM on the non-whitelisted internal network subnet.

The downside of such an approach is that port mappings to running containers on the VM could become cumbersome to manage. I don't have a great solution for that one at this time.

Thoughts?