Wrong Batch Transform exit code for failed jobs

[ilazakis]

When a batch transform job fails, Sagify still returns a 0 exit code.

We need to check the SageMaker status returned here and exit with 1 or similar if the status is Failed (not sure if we can future proof this in case SageMaker changes the literal from Failed to something else but should be easy to catch).

[pm3310]

#98