Summary:
Pull Request resolved: https://github.com/facebook/react-native/pull/48440
Changelog: [internal]
Modifies the Fantom runner to read 2 new environment variables to help with debugging:
- `FANTOM_PRINT_OUTPUT`: prints the output of the CLI to the output of the test.
- `FANTOM_LOG_COMMANDS`: logs the buck commands executed by the runner, so they can be re-run outside the runner for debugging, etc.
Reviewed By: rshest
Differential Revision: D67682750
fbshipit-source-id: aff48c4f47078db1be53e0ee105089fbc921768f