fixed 'too many file open' & removed useless codes
Squashed commit of the following:

commit 757ee8c695c45a7b69b86c7d67c3990091c0ffa5
Merge: 648336e 48a44a7
Author: 김형준 <babokim@babokim-MacBook-Pro.local>
Date:   Mon Jun 16 16:51:11 2014 +0900

    Merge branch 'taskAlloc' of https://github.com/jinossy/tajo into multiple-fifo-queue

    Conflicts:
    	tajo-core/src/main/java/org/apache/tajo/scheduler/AbstractScheduler.java
    	tajo-core/src/main/java/org/apache/tajo/scheduler/MultiQueueFiFoScheduler.java
    	tajo-core/src/main/java/org/apache/tajo/scheduler/Scheduler.java
    	tajo-core/src/main/resources/webapps/admin/scheduler.jsp

commit 648336ea533587165c937d24f213cf6a70619069
Author: 김형준 <babokim@babokim-MacBook-Pro.local>
Date:   Mon Jun 16 12:29:20 2014 +0900

    Add multiple fifo queue.