Dockerfile - split package install/build into separate step

So one it's done, changes to later steps don't need to re-do it. It's slow!

Dockerfile

@@ -63,26 +63,29 @@ RUN \
       Mopidy-MPD \
       Mopidy-Spotify-Web \
       Mopidy-SoundCloud \
-  && echo "* Creating Mopidy User" \
+  && echo "* Cleaning up" \
+    && rm -rf /var/cache/apk/* \
+    && rm -rf /tmp/*
+
+# Do this in a separate layer, because building the last is slooow
+# This allows us to alter these parameters without rebuilding the last.
+RUN \
+  echo "* Creating Mopidy User" \
     && addgroup -g ${pgid} mopidy \
     && adduser -h /mopidy -s /bin/sh -D -G mopidy -u $puid mopidy \
     && delgroup audio \
     && addgroup -g ${audio_gid} audio \
     && addgroup mopidy audio \
-    && echo "mopidy ALL=NOPASSWD: /usr/local/lib/pyenv/versions/*/lib/python*/site-packages/mopidy_iris/system.sh" >> /etc/sudoers \
-  && echo "* Cleaning up" \
-    && rm -rf /var/cache/apk/* \
-    && rm -rf /tmp/* \
-  && echo "* Ready to start Mopidy" \
+    && echo "mopidy ALL=NOPASSWD: /usr/lib/python3.8/site-packages/mopidy_iris/system.sh" >> /etc/sudoers \
+  && echo "* Done" \
   && sleep 1
 
 COPY   root/ /
-RUN    chmod +x /usr/local/bin/run.sh
-RUN    chmod +x /usr/local/bin/entrypoint.sh
+RUN    chmod +x /usr/local/bin/run.sh /usr/local/bin/entrypoint.sh
 EXPOSE 6600 6680 8000
 VOLUME /data /music
 
 LABEL description "Open source media server"
 
 ENTRYPOINT ["entrypoint.sh"]
-CMD ["run.sh"]
+#CMD ["run.sh"]