SQOOP-845: Improve Generic JDBC validator

(Jarcec Cecho via Cheolsoo Park)
SQOOP-851: NullPointerException in Mapreduce Submission engine initialization

(Jarcec Cecho via Cheolsoo Park)
SQOOP-850: Move server initialization from server module to core

(Jarcec Cecho via Cheolsoo Park)