Change error logging for an error we're suppressing to debug logging

@stephensanchez This really scary error message was showing up in the worker logs while I was testing.  However, it looks like the error occurs when running cross-validation, so even if this exception occurs, the classifiers will still be trained successfully.  EASE seems to be swallowing the exception, but logging it as an error, so I've downgraded the logging to a debug statement.