TAJO-1038: Remove use of Builder variable in Schema.

Closes #140
TAJO-1034: Reduce Explicit Use of JVM Internal Class. (Jihun Kang via hyunsik)
TAJO-1024: RpcConnectionPool::getConnection can cause NPE at initialization.

Closes #139
TAJO-1037: KillQuery hang in subquery init state. (jinho)

Closes #137
TAJO-1015: Add executionblock event in worker. (jinho)

Closes #124
TAJO-1040: Misuse netty HashedWheelTimer. (jinho)
TAJO-1048: Missed use of session variables in GlobalPlanner.

Closes #146
TAJO-948: 'INSERT INTO' statement to non existence table casuses NPE. (Jongyoung Park via hyunsik)

Closes #142
TAJO-910: Simple query (non-forwarded query) should be supported against partition tables.
Fix eval difference partitioned column value bug.
Merge branch 'master' of https://git-wip-us.apache.org/repos/asf/tajo into TAJO-910