TAJO-1221: HA TajoClient should not connect TajoMaster at the first. (jaehwa)

Closes #286
TAJO-1254: Fix getProgress race conditions in Query. (jinho)

Closes #304
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-1250
TAJO-324: Rename the prefix 'QueryUnit' to Task.

Closes #306
TAJO-1232: Implicit groupby queries with LIMIT lead to wrong results. (jihoon)
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-1250