TAJO-793: CLI should be able to exit when single query is failed. (Hyoungjun Kim via jinho)

Closes #25
TAJO-854: Supports INSERT INTO with UNION. (Hyoungjun Kim via jihoon)
TAJO-849: Add Parquet storage to HCatalogStore. (jaehwa)
TAJO-853: Refactoring FilterPushDown for OUTER JOIN
Add NullScannler which returns null if a table has not any data files.
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-853