Update file Dockerfile

gitlab-ci/Dockerfile

@@ -4,6 +4,7 @@ FROM sdvharbor.slub-dresden.de/replication/debian:${DEBIAN_RELEASE}-slim
 # Do NOT delete "ARG DEBIAN_RELEASE" line, it's needed because of 
 # https://docs.docker.com/engine/reference/builder/#understand-how-arg-and-from-interact
 ARG DEBIAN_RELEASE
+ARG VERBOSE=true
 ARG GITDIR
 ENV DEBIAN_FRONTEND=noninteractive
 ENV EXTDPKG="extdpkg"