Ensure /etc/clickhouse-server is readable

Dockerfile

@@ -13,7 +13,9 @@ RUN apt-get -q update \
     && apt-get -q remove --purge -y ca-certificates \
     && apt-get -q autoremove -y \
     && apt-get -q clean \
-    && rm -fr /var/lib/apt/lists/*
+    && rm -fr /var/lib/apt/lists/* \
+    && chown -R root:root /etc/clickhouse* \
+    && chmod -R a+rX /etc/clickhouse*
 
 ENTRYPOINT ["/usr/bin/clickhouse-server", "--config=/etc/clickhouse-server/config.xml"]