Fix executorch/exir/tests:quantization (#243)

Summary:
Pull Request resolved: https://github.com/pytorch/executorch/pull/243

Seems like it is failing for a while

Error ModuleNotFoundError: No module named 'expecttest'

Fixed by importing directly

After that, had to add export_program

Reviewed By: jerryzh168

Differential Revision: D49058674

fbshipit-source-id: 7beb9597fa7bddc32fb0d73bdc32cd8995ba3c96