Expose test artifacts to the Gitlab CI interface

Make tests generate JUnit artifacts and expose them to the Gitlab CI UI.

test/Dockerfile

 FROM debian:stable
 
 RUN apt-get -q update && env DEBIAN_FRONTEND=noninteractive \
-    apt-get install --no-install-recommends -y python3 python3-pip python3-setuptools python3-yaml python3-jinja2 python3-nose python3-dnspython
+    apt-get install --no-install-recommends -y python3 python3-pip python3-setuptools python3-yaml python3-jinja2 python3-pytest python3-dnspython
 
 ADD . /src
 WORKDIR /src
@@ -9,4 +9,4 @@ RUN python3 setup.py install
 
 ENV TEST_CONFIG=/test-config.yml
 ENV TEST_PARAMS=/src/float_integration_test/test-params.yml
-CMD ["nosetests3", "-v", "float_integration_test"]
+CMD ["pytest", "-v", "-junit_xml=/artifacts/pytest.xml", "float_integration_test"]