poweroff: fix bug in orderly_poweroff()

poweroff: fix bug in orderly_poweroff()

orderly_poweroff is trying to poweroff platform by two steps:

step 1: Call userspace application to poweroff

step 2: If userspace poweroff fail, then do a force power off if force
param is set.

The bug here is, step 1 is always successful with param UMH_NO_WAIT,
should change to UMH_WAIT_EXEC which will monitor whether user application
successful run.

Signed-off-by: Feng Hong <hongfeng@marvell.com>
Acked-by: Kees Cook <keescook@chromium.org>
Cc: Serge Hallyn <serge.hallyn@canonical.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: "Rafael J. Wysocki" <rjw@sisk.pl>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>