Get child processes before main process die

Signed-off-by: Alexander Morozov <lk4d4@docker.com>

Docker-DCO-1.1-Signed-off-by: Jessie Frazelle <jess@docker.com> (github: jfrazelle)

Docker-DCO-1.1-Signed-off-by: Jessie Frazelle <princess@docker.com> (github: jfrazelle)

daemon/execdriver/native/driver.go

@@ -189,6 +189,8 @@ func waitInPIDHost(p *libcontainer.Process, c libcontainer.Container) func() (*o
 			return nil, err
 		}
 
+		processes, err := c.Processes()
+
 		process, err := os.FindProcess(pid)
 		s, err := process.Wait()
 		if err != nil {