to not mix with sample config.

See solsson/dockerfiles#10.

of not forwarding signals as Alpine did.
Kafka logs say nothing, and after 30s the container is terminated.
With /bin/bash instead the log indicates shutdown behavior.

This reverts commit c188f43.

modify config prior to kafka start. My aim with this is to
get rid of the /bin/sh startup scripts and use bin + args directly.

avoiding a layer of indirection and the associated gotchas with signals.