E2e android

Summary:- converted shell script `scripts/e2e-test.sh` into JS script to have more programming flexibility
- using appium execute 2 tests after a fresh React Native app installation: check HMR and that debugging mode does not crash the app
- made sure tests can be stable on limited CI systems and added ways to debug any problems in the future

Using appium we can now interact with Android app and test its state.
As a follow up i am planning to write a blog post on how to use appium with android and ios for e2e testing.
Closes https://github.com/facebook/react-native/pull/6840

Differential Revision: D3173635

Pulled By: mkonicek

fb-gh-sync-id: 3cf044bc9f64d1a842ae4589dd1bcab76de3d66a
fbshipit-source-id: 3cf044bc9f64d1a842ae4589dd1bcab76de3d66a