Updating kafka scripts with recent changes from 0.8 branch.

- debian/bin/kafka now incorporates changes to kafka-run-class.sh
  that allow for easier overriding of many Kafka environment variables.
- debian/kafka*.init now use debian/bin/kafka script to start kafka
  services, rather than hardcoding the classpath and default environment
  variables multiple times.  

Change-Id: I4b92b94a71efdd03970b17679274386b512c8b50