Slightly cleaner installation

kafka/Dockerfile

@@ -4,6 +4,7 @@ FROM solsson/kafka-jre@sha256:7765513cf5fa455a672a06f584058c1c81cc0b3b56cc56b0cf
 ENV KAFKA_VERSION=0.11.0.0 SCALA_VERSION=2.11
 
 RUN set -ex; \
+  export DEBIAN_FRONTEND=noninteractive; \
   runDeps='netcat-openbsd'; \
   buildDeps='curl ca-certificates'; \
   apt-get update && apt-get install -y $runDeps $buildDeps --no-install-recommends; \
@@ -12,6 +13,8 @@ RUN set -ex; \
   mkdir -p /opt/kafka; \
   curl -SLs "https://www-eu.apache.org/dist/kafka/$KAFKA_VERSION/kafka_$SCALA_BINARY_VERSION-$KAFKA_VERSION.tgz" | tar -xzf - --strip-components=1 -C /opt/kafka; \
   \
+  rm -rf /opt/kafka/site-docs; \
+  \
   apt-get purge -y --auto-remove $buildDeps; \
   rm -rf /var/lib/apt/lists/*; \
   rm -rf /var/log/dpkg.log /var/log/alternatives.log /var/log/apt