Created by: luotao1

1. 修复了test_layerHelpers在第二次运行时出现的以下bug

diff:/home/luotao/Paddle/python/paddle/trainer_config_helpers/tests/configs/protostr/img_layers.protostr.unittest.unittest: No such file or directory

2. 修改了build_docker_image.rst中几处字词问题。