Fixes bug where using Execution the Hive sources no longer append data.

The hack we do in the Hive parquet sources no longer works so this is a work around. The benefit this has is that we can now choose which sources are append and which one's aren't.
I'm reworking it. However, there is a bigger problem in that the unpartitioned approach doesn't actually have any support for append.

@mnikliborc did you look into this at all? What does the append flag do for HiveParquetScroogeSource?