First, if we can't open dd_cwd, we leak opened dd_root.

Second, if chroot(dd_root) fails, we leak opened dd_cwd.

Instead of adding more close() statements in place, let's
change the code to close both fds on exit path.

Reported by Coverity, CID 51639, CID 51631.
Signed-off-by: Kir Kolyshkin <kir@openvz.org>
Acked-by: Andrew Vagin <avagin@odin.com>
Signed-off-by: Pavel Emelyanov <xemul@parallels.com>