add wait4 after kill

Docker-DCO-1.1-Signed-off-by: Victor Vieux <vieux@docker.com> (github: vieux)

daemon/execdriver/native/driver.go

@@ -187,6 +187,7 @@ func (d *driver) Terminate(p *execdriver.Command) error {
 	}
 	if started == currentStartTime {
 		err = syscall.Kill(p.Process.Pid, 9)
+		syscall.Wait4(p.Process.Pid, nil, 0, nil)
 	}
 	d.removeContainerRoot(p.ID)
 	return err