Rework (default) init.d script, again

* Store environment variables in /etc/sysconfig/kafka. Might be blasphemy to use 'export' in these files, but I haven't seen anything about it though.
* Source /etc/sysconfig/kafka in init.d script.
* Try to stop kafka by sending a SIGINT and then TERM&KILL. The stop script that is bundled with kafka uses SIGINT, so why not.
Correct configure spec w.r.t to new init.d script layout
Add init.d script for the debian platform
Add debian to supported OSes