Bentoml: Add integration tests for FastAI

[parano]

Currently, FastAI artifact code is not tested: https://codecov.io/gh/bentoml/BentoML/tree/master/bentoml/frameworks

We would want to add an integration test suit to test its functionalities including save, load, and run inference from API server. The setup should be similar to other integration tests that can be found here: https://github.com/bentoml/BentoML/tree/master/tests/integration

[xiwang129]

Hi, I would like to work on this one. thank you!

[yubozhao]

@xiwang129 Any update? Let me know if you need any help