chore(Dockerfile): cleanup after installation a bit more than before …

…and keep copyright / license files (#113)

rootfs/Dockerfile

@@ -8,8 +8,25 @@ RUN addgroup --quiet --gid 2000 slug && \
 RUN sed -i -e 's/^deb-src/#deb-src/' /etc/apt/sources.list && \
     apt-get update && \
     apt-get install -y md5deep && \
-    apt-get clean && \
-    rm -rf /var/lib/apt/lists/* /tmp/* /var/tmp/* /usr/share/man /usr/share/doc && \
+    # cleanup
+    apt-get autoremove -y && \
+    apt-get clean -y && \
+    # package up license files if any by appending to existing tar
+    COPYRIGHT_TAR='/usr/share/copyrights.tar'; \
+    gunzip $COPYRIGHT_TAR.gz; tar -rf $COPYRIGHT_TAR /usr/share/doc/*/copyright; gzip $COPYRIGHT_TAR && \
+    rm -rf \
+        /usr/share/doc \
+        /usr/share/man \
+        /usr/share/info \
+        /usr/share/locale \
+        /var/lib/apt/lists/* \
+        /var/log/* \
+        /var/cache/debconf/* \
+        /etc/systemd \
+        /lib/lsb \
+        /lib/udev \
+        /usr/lib/x86_64-linux-gnu/gconv/IBM* \
+        /usr/lib/x86_64-linux-gnu/gconv/EBC* && \
     bash -c "mkdir -p /usr/share/man/man{1..8}"
 
 ADD . /