Use an updated version of kafka for the datahub kafka-setup image

Previously, we have used the thirdparty/confluent component when
building our kafka-setup image, but this has proven to be incompatible
with the scripts that configure kafka for datahub.

In response to this we added a thirdparty/confluent7 component, which
enables access to version 3.4 of Kafka.

Bug: T329514
Change-Id: Id7aae5f02e3fcb5e927eab52d340cf372f8c3b1f