Turn off verbose output from tar extraction when building docker files, fixes #15528

packaging/docker/Dockerfile

@@ -9,7 +9,7 @@ RUN apt-get update && apt-get install -qq -y tar && \
 
 COPY ${GRAFANA_TGZ} /tmp/grafana.tar.gz
 
-RUN mkdir /tmp/grafana && tar xfvz /tmp/grafana.tar.gz --strip-components=1 -C /tmp/grafana
+RUN mkdir /tmp/grafana && tar xfz /tmp/grafana.tar.gz --strip-components=1 -C /tmp/grafana
 
 ARG BASE_IMAGE=debian:stretch-slim
 FROM ${BASE_IMAGE}