Fix/Improve daemon script

After creating distribution package using following command,

```
mvn package -Pbuild-distr 
```

Zeppelin can not find zeppelin-web*.war and fails to load web ui.
This PR fix the problem and improve zeppelin-env.sh little bit.

* [x] Fix problem finding zeppelin-web*.war
* [x] Let user define JVM mem option in zeppelin-env.sh

Ready to merge.