Summary:
- Consolidate common code in iOS and tvOS test scripts
- Start the packager before starting tests, to improve reliability
- Increase timeout value in RCTTestRunner.m
Closes https://github.com/facebook/react-native/pull/10378
Differential Revision: D4028364
Pulled By: bestander
fbshipit-source-id: 24c2124a1c62643a02f0668b60a67b971e08d1a3