Fix dependencies and tests for clean Python 2 & 3 test runs under Docker.

This change gives a clean test run in the Debian-based Python 2 and Python 3
docker images.

Dockerfile-debian-python2-sqlite

@@ -24,7 +24,9 @@ python-py \
 python-pytest \
 python-pytest-xdist \
 python-six \
+python-snowballstemmer \
 python-sphinx \
+python-sphinxcontrib.websupport \
 python-webtest
 
 RUN apt-get install -y \
@@ -58,6 +60,8 @@ RUN ./bootstrap.sh
 RUN VIRTUALENV_FLAGS='--system-site-packages' ./configure --without-python3
 RUN make
 
+RUN ./bin/python -m pytest ./mediagoblin/tests --boxed
+
 RUN echo '[[mediagoblin.media_types.audio]]' >> mediagoblin.ini
 RUN echo '[[mediagoblin.media_types.video]]' >> mediagoblin.ini