Unified command execution in Docker containers.

Also adds a hotfix for a broken test execution based on
an issue with a used library: https://github.com/pytest-dev/pytest/issues/4770

Change-Id: I54aade1eda31cb2584641b95226fbf39d9d298f4
Signed-off-by: peusterm <manuel.peuster@uni-paderborn.de>
diff --git a/Dockerfile b/Dockerfile
index 4b8627a..cccecdf 100755
--- a/Dockerfile
+++ b/Dockerfile
@@ -58,6 +58,9 @@
 WORKDIR /son-emu
 RUN python setup.py develop
 
+# Hotfix: https://github.com/pytest-dev/pytest/issues/4770
+RUN pip2 install "more-itertools<=5.0.0"
+
 # Important: This entrypoint is required to start the OVS service
 ENTRYPOINT ["/son-emu/utils/docker/entrypoint.sh"]
 CMD ["python", "examples/default_single_dc_topology.py"]