fail make target when docker wait returns with non zero output (#184)

just install python3-minimal in base
clear apt key todo
rework test-ci to fail when the test containers exits with error code != 1

zpush/Dockerfile

@@ -43,6 +43,7 @@ RUN \
     echo "deb [${KOPANO_REPOSITORY_FLAGS}] ${KOPANO_CORE_REPOSITORY_URL} ./" > /etc/apt/sources.list.d/kopano.list; \
     # prepare z-push installation
     echo "deb ${KOPANO_ZPUSH_REPOSITORY_URL} /" > /etc/apt/sources.list.d/zpush.list && \
+    # this is the same key as for the rest of the Kopano stack, making a separate download anyways as this may not be the case in the future 
     curl -s -S -o - "${KOPANO_ZPUSH_REPOSITORY_URL}/Release.key" | apt-key add - && \
     # install
     set -x && \