Revert regression introduced in 81eac415ad, which caused 'docker run -i' to never close stdin

commands.go

@@ -927,6 +927,7 @@ func (srv *Server) CmdRun(stdin io.ReadCloser, stdout io.Writer, args ...string)
 		if !config.Detach {
 			Go(func() error {
 				_, err := io.Copy(cmdStdin, stdin)
+				cmdStdin.Close()
 				return err
 			})
 		}