qgen: make correctness triaging either by running impala with -convert_legacy_hive_parquet_utc_timestamps=true

Being relatively new, I was triaging query generator correctness discrepancies and came across a problem in which some timestamp columns had different hours in Impala vs. Postgres. Taras helpfully pointed out this was a known issue, fixed via -convert_legacy_hive_parquet_utc_timestamps=true.

While we can debate about how to properly load the data or other strategies, let's reduce false positive correctness issues and run Impala in the query generator with -convert_legacy_hive_parquet_utc_timestamps=true all the time.