This patch fixes an exit code if a page-server is started
as a daemon. Now the criu exits with a pid of a page server,
it's meaningless, because pid is usually bigger than 128.

travis-ci: success for series starting with [1/2] page-server: don't return a server pid from page-server
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>
Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>