page-server creates a listen socket and only then goes into the
background, so we can be sure, that page-server is ready for work after
detaching.

v2: call daemon() in a proper place and reuse the option -d
Signed-off-by: Andrey Vagin <avagin@openvz.org>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>