Update Zeppelin shell scripts

I suggest Zeppelin use a consistent shell styleguide to make code easier to read\understand and less bug-prone.
Can you tell me why did you remove nohup and nice?

check original code, how zeppelin is started.
```
nohup nice -n $ZEPPELIN_NICENESS $ZEPPELIN_RUNNER $JAVA_OPTS -cp $CLASSPATH $ZEPPELIN_MAIN "$@" >> "$log" 2>&1 < /dev/null &
```