follow docker guidelines

contrib/docker/runtime/Dockerfile

@@ -1,20 +1,24 @@
 FROM debian
 
-RUN apt-get update
-RUN apt-get install -y curl libmosquitto1
+RUN apt-get update && apt-get install -y \
+    libmosquitto1 \
+    curl
 
 LABEL maintainer "ebusd@ebusd.eu"
 
+ENV EBUSD_VERSION 3.0pre
+ENV EBUSD_ARCH amd64
+
+LABEL version "${EBUSD_VERSION}-${EBUSD_ARCH}-mqtt1"
+
+COPY ebusd-${EBUSD_VERSION}_${EBUSD_ARCH}_mqtt1.deb ebusd.deb
+
+RUN dpkg -i ebusd.deb
+
 RUN mkdir /etc/ebusd \
     && curl -SL https://github.com/john30/ebusd-configuration/archive/master.tar.gz \
     | tar xz --strip-components=3 -C /etc/ebusd ebusd-configuration-master/ebusd-2.1.x/de
 
-ENV EBUSD_VERSION 3.0pre
-ENV EBUSD_ARCH amd64
-COPY ebusd-${EBUSD_VERSION}_${EBUSD_ARCH}_mqtt1.deb ebusd.deb
-
-RUN dpkg -i ebusd.deb
-
 EXPOSE 8888
 
 COPY docker-entrypoint.sh /