Also now permit interactivly running tests without explicitly setting
$srcdir. This now works if we are inside ./tests and fails, as before,
when we are in a different directory.
Detected by shellcheck via CodeFactor.io
- Removed all sleeps where possible.
- Moved all kafka start/stop/download logic into functions.
- Moved kafka/zookeeper stop into error_exit and exit_test.
- Kafka/Zookeeper cleanup only done on success now.
- Kafka/Zookeeper logfiles automatically dumped on error_exit only now.
- Added cleanup for Kafka/Zookeeper instances into CI/buildbot_cleanup.sh