Update Zeppelin shell scripts

I suggest Zeppelin use a consistent shell styleguide to make code easier to read\understand and less bug-prone.
Honestly, I am not sure about `nohup` for a deamon script, what i learn and read on the internet is that `nohup` is mainly use for interactive shell, it has a controlling terminal and will receive a `SIGHUP (hangup)` signal when the controlling process (typically your shell) exits. `nohup` command arranges for input to come from /dev/null.
For example on your sheel you start firefox but you want him to stay alive if you close | exit your shell, so you will do something like `nohup firefox& &> /dev/null`, witch is really different from a deamon 


If you need more accurate ressource, here some references : 
 * Stevens' 'Advanced Programming in the UNIX Environment'
 * 'UNIX Network Programming (3rd Edn)'
 * Rochkind's 'Advanced UNIX Programming'