Add init script to the debian packaging

This patch add init scripts to the debian packaging

The debian package has been renamed to apache-spark because a package spark already exists:
http://packages.ubuntu.com/trusty/spark

I'm not an expert in init script, most of the code has been inspired by the ones for elasticsearch and cassandra.

It seems that usual init script relies on a predefined function start-stop-daemon. Since the daemonization is already handled by spark's scripts, in order to avoid a refactoring, I tried to make the best of not modifying much spark scripts.