Convert NOCHECKIN from up-front suite failure to test failure to unblock diagnosing build/test issues on CI

https://github.com/DynamoRIO/dynamorio/wiki/Code-Style suggests to mark temporary code unsuited for committing with NOCHECKIN. However, if you do that, the builds fail, making it unsuitable for testing e.g. on Travis.

If NOCHECKIN would prevent the code being able to merge (pre-commit hook on Travis?), it would make sense. Otherwise I'm not sure how the NOCHECKIN hook could be used for as long as we're using Travis.