Make the backdoor port (8084 by default) only listen on "localhost"

I consider the way how Traffic Server opens listening ports dangerous, or at least more risky than necessary. Currently ATS allows to configure port numbers for the related services, but not the listening interface. Instead it binds to 0.0.0.0. Therefore I'd like to suggest

• Allow the user to specify a listening interface, don't assume 0.0.0.0 suits for all setups.
• Disable the "autoconfiguration port" (i.e. 8083 by default) unless proxy.local.cluster.type is set to enable clustering (!= 3). I think traffic_shell and eventually traffic_line use this port to configure ATS locally. If so it should be bound to the loop back at least or using Unix Domain Sockets or whatever local socket method you prefer.
• Disable the "reliable service port" (i.e. 8088 by default) unless proxy.local.cluster.type enables clustering. Similar to the "autoconfiguration port". If traffic_cop (or something else on the local machine) is using this port, the same suggestions apply as above.
• The "internal communication port" (8084) should not open a public socket at all. Instead use Unix Domain Sockets or something similar.