upstreamed: https://github.com/docker/docker/pull/28454

do not require custom build of tini

https://github.com/krallin/tini/issues/55#issuecomment-260507562

host# docker run --init --rm -it glen/pld bash -l
bash-4.4# /dev/init -- sh -c 'echo "kala" "maja"; cat /proc/$$/cmdline|tr "\0" "\n">cmdline'
[WARN  tini (39)] Tini is not running as PID 1 and isn't registered as a child subreaper.
Zombie processes will not be re-parented to Tini, so zombie reaping won't work.
To fix the problem, use the -s option or set the environment variable TINI_SUBREAPER to register Tini as a child subreaper, or run Tini as PID 1.
kala maja
bash-4.4# cat cmdline
sh
-c
echo "kala" "maja"; cat /proc/$$/cmdline|tr "\0" "\n">cmdline
bash-4.4#

--- docker-1.13.0-rc1/daemon/oci_linux.go~	2016-11-11 12:27:33.000000000 +0200
+++ docker-1.13.0-rc1/daemon/oci_linux.go	2016-11-15 02:42:25.660635864 +0200
@@ -593,7 +593,7 @@
 	if c.HostConfig.PidMode.IsPrivate() {
 		if (c.HostConfig.Init != nil && *c.HostConfig.Init) ||
 			(c.HostConfig.Init == nil && daemon.configStore.Init) {
-			s.Process.Args = append([]string{"/dev/init", c.Path}, c.Args...)
+			s.Process.Args = append([]string{"/dev/init", "--", c.Path}, c.Args...)
 			var path string
 			if daemon.configStore.InitPath == "" && c.HostConfig.InitPath == "" {
 				path, err = exec.LookPath(DefaultInitBinary)