TAJO-842: NULL handling in JDBC. (Hyoungjun Kim via jinho)

Closes #18
TAJO-842: NULL handling in JDBC. (fixed a missing log in CHANGES)
TAJO-846: Clean up the task history in woker. (jinho)

Closes #20
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-762: Implements current date/time function (Hyoungjun Kim via hyunsik)

Closes #16
TAJO-863: Column order mismatched in the JOIN query with asterisk selection. (Hyoungjun Kim via hyunsik)

Closes #31
TAJO-843: implements COALESCE for BOOLEAN, DATE, TIME, TIMESTAMP. (Hyoungjun Kim via hyunsik)

Closes #26
TAJO-860: Implements TRUNCATE table. (Hyoungjun Kim via hyunsik)
TAJO-860: Implements TRUNCATE table. (missed github closes)

Closes #29, #24.
TAJO-868: TestDateTimeFunctions unit test is occasionally failed.

Closes #34
TAJO-858 - Support for hadoop kerberos authentication in Tajo

Replaced normal getFileSystem method with FileSystemUtil.getFileSystem
at few places in the codebase.
Merge remote-tracking branch 'origin/master' into tajo-858