[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}'
Merge pull request #62 from kraman/foreground_exec_socket_act

[WIP] Socket activated containers