Add daemon option
Ignore SIGHUP with --daemon specified
Show warning if log output is tty in daemon mode
Change daemonize timing after zookeeper started
Functionize daemonization
Add daemon mode to jubaproxy
fork() and setsid() in daemon mode
Revert "fork() and setsid() in daemon mode"

This reverts commit 13f9ed234db152fa3455de9c2d4cd9634a233d51.
(fork() and setsid() should be considered in another pull-request)
Merge pull request #569 from gintenlabo/add-daemon-mode

Add daemonize option (implements #409)