Batch retrieval fails to catch certain errors

[zhilingc]

Batch retrieval for BQ fails to catch the following errors:

1. Loading entity dataset into BQ
2. Allocating UUIDs for rows in the entity dataset

# BigQueryServingService.java

  public GetBatchFeaturesResponse getBatchFeatures(GetBatchFeaturesRequest getFeaturesRequest) {
    ....
    // here
    Table entityTable = loadEntities(getFeaturesRequest.getDatasetSource());
    ....
    // and here
    TableId entityTableWithUUIDs = generateUUIDs(entityTable);
    String entityTableName = generateFullTableName(entityTableWithUUIDs);
    ....
  }

As a result when retrieving using the python sdk the sdk polls forever, unbeknownst to the error.