Otherwise sigchld_handler() will call waitpid()
and worries about unknown process.

(00.333012)      1: kernel/hostname nr 15
(00.333120)      1: kernel/domainname nr 6
(00.335243)      1: Error (cr-restore.c:1225): BUG at cr-restore.c:1225

v2: don't use unitialized oldmask

Cc: Tycho Andersen <tycho.andersen@canonical.com>
Reported-by: Mr Jenkins
Signed-off-by: Andrew Vagin <avagin@openvz.org>
Acked-by: Tycho Andersen <tycho.andersen@canonical.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>