Set the GID for varnish in the klarlack container to agree with haproxy.

For the Unix domain socket over which haproxy and varnish communicate,
we have chmod 660 and chgrp varnish. haproxy belongs to group varnish
and thus has write permissions on the socket, which is required in
Linux to be able to connect.

For that, both containers must have the same group name and GID.
We've been using 998, since that results from the RPM install for
Varnish from the official packagecloud repos.

container/Dockerfile.klarlack

@@ -32,7 +32,10 @@ RUN apt-get install -y dcs-classifier \
     varnish-modules \
     varnish-objvar
 
-RUN /bin/mkdir /var/run/varnish
+# Set the varnish GID to 998 as in the packagecloud install.
+RUN /bin/mkdir /run/varnish && \
+    /usr/sbin/groupmod -g 998 varnish
+
 COPY bogo_backend.vcl /etc/varnish/
 COPY ready.vcl /etc/varnish/
 COPY notavailable.vcl /etc/varnish