Add `automatic_start` attribute

When set to true, `:start` will be added to the `action` array that is
given to the kafka service definition.
Restart kafka on server configuration file change

One could argue that it should restart if env configuration file changes
as well, and probably log4j configuration. Coming up next.
Additional configuration to consider for automatic restart

* /opt/kafka/log4j.properties
* /etc/init.d/kafka
* /etc/sysconfig/kafka

And the corresponding files depending on platform and init style.
Start kafka automatically if `automatic_restart` is set

Now, I’m not a fan of starting / restarting things automatically as it
tends to break things, but this feels quite natural to me. No?
`automatic_restart` implies `automatic_start`

Reasoning stated in the comment.
Merge branch 'automatic-start-restart'

Closes #42.