Connection handling in ZeppelinDriver changed to ThreadLocal to avoid syncronization
small cleanup - removed comments and re-arranged LTest a bit
Merge branch 'refactoring-zengine' into multiple_driver

Conflicts:
	zeppelin-driver-hive11/src/main/java/com/nflabs/zeppelin/driver/hive11/HiveZeppelinDriver.java
	zeppelin-server/src/main/java/com/nflabs/zeppelin/server/ZQLJob.java
	zeppelin-zengine/src/main/java/com/nflabs/zeppelin/driver/ZeppelinDriver.java
	zeppelin-zengine/src/test/java/com/nflabs/zeppelin/zengine/api/LTest.java