[WIP] Socket activated containers

For containers which require the socket proxy:

    curl -X PUT "http://localhost:8080/token/__test__/container?t=pmorie%2Fsti-html-app&r=0001" -d '{"ports":[{"external":4343,"internal":8080}],"socket_activation":true}'

For containers which support file descriptor based sockets:

    curl -X PUT "http://localhost:8080/token/__test__/container?t=pmorie%2Fsti-html-app&r=0001" -d '{"ports":[{"external":4343,"internal":8080}],"socket_activation":true,"dont_proxy_socket":true}'

NOTE: Socket activation requires the docker fork-exec + libcontainer branch:
https://github.com/kraman/docker/tree/forking-run-kr