Reimplement bin/kafka-start

- Dynamically wait for zk/kafka instead of fixed two second sleep
- Capture zk/kafka output into log-files
- Use bundle show kafka-jars to figure out location of zk/kafka jars
- Avoid uppercase letters for non-exported shell variables
Avoid running specs in jruby-head

It seems to fail more often than not.
No need to stop kafka after

Travis will kill the whole machine in any case.
Capture any log output after starting kafka

This should hopefully simplify debugging of future failures
Merge branch 'grddev-travis-setup'