Created by: luotao1

• cache the download of se_resnext50 ocr mobilenet to /root/.cache/inference_demo
• remove tar -czf fluid.tgz fluid in PR CI, only do it in nightly manylinux1 job. since it cost 4 mintues to do tar -czvf.

[11:50:53][Step 1/1] + cp -r fluid_install_dir fluid
[11:50:59][Step 1/1] + tar -czf fluid.tgz fluid
[11:54:52][Step 1/1] + test_fluid_inference_lib