Continue fixing deadlock of previous commit, this time occuring when waiting for 'cleanup' python runtime call to finish. Now 'init' and 'cleanup' python runtime calls are called directly from main thread, and aren't anymore invoked in the context of wxMainloop and/or twisted reactor.
#
# Dockerfile for wxPython3.0 running on python2.7
#
FROM python:2.7-stretch
RUN set -xe \
&& apt-get update \
&& apt-get install -y --no-install-recommends python-wxgtk3.0 python-matplotlib \
&& apt-get install -y --no-install-recommends python-xvfbwrapper xvfb \
&& apt-get clean