Docker build broken

[j-maas]

It seems like the Debian running under the hood of python:3.4-slim has been updated, such that the packages libmysqlclient-dev and npm are not found. Choosing a base image that still uses Jessie (e. g. python:3.5-slim-jessie) fixes the issue for me.

However, the build still fails at the install step, because some packages do not install properly.

Errors were encountered while processing:
 postgresql-client-9.4
 postgresql-client
E: Sub-process /usr/bin/dpkg returned an error code (1)