Adds KAFKA_TAG env var and sets default as 2.11-1.0.2

Kafka image was being pulled from latest, which generated
incompatibilities with kafka clients used in modules.
It has been modified to pull from the latest supported version,
which is 1.0.2. In case there is a need to use another image tag,
it can be done through KAFKA_TAG env var.

Signed-off-by: Benjamin Diaz <bdiaz@whitestack.com>