cmdserver: wrap 'pipe' mode server by service object
This is the stub for new mode that will listen for connections on unix domain
socket.
Though --daemon option is not banned in 'pipe' mode, it is useless because
the detached 'pipe' mode server exits immediately due to null stdin. Should
it abort if --daemon is specified with --cmdserver pipe or --stdio?
Hello, Foobar
['Hello, Fo, =;o', 'Hello, Bar']