The current travis-ci job would fail only if the last command failed. It would be succeed if other commands than the last one fail.
This PR execute the script in another shell instance, so we should export those variables and bash functions. It would return 1 if the script fail no matter if it's the last command.
Sorry for ruin the travis ci system in #14231
Test: https://travis-ci.org/ken2812221/bitcoin/jobs/467086010