Add support for AnalysisBaseExternals Python 2.7 and Python 3 in same environment (!29)

Resolves #4 (closed)

Unset PYTHONHOME and PYTHONPATH and add supporting Python .pth file

As PYTHONHOME and PYTHONPATH are unset then a AnalysisBaseExternals_python2.pth file needs to be added for the AnalysisBase Externals Python 2.7 to be used along with ROOT in the same environment as Python 3

atlasml-base/Dockerfile

@@ -40,6 +40,11 @@ if [ -f /opt/_h5ls/_h5ls.sh ]; then\n\
 fi'\
 >> ${HOME}/.bashrc
 
+# Get AnalysisBase Python 2.7 and Python 3 working in same environment
+RUN printf "\nunset PYTHONHOME\nunset PYTHONPATH\n" >> /home/atlas/release_setup.sh && \
+    source /home/atlas/release_setup.sh && \
+    echo "${AnalysisBaseExternals_DIR}/lib" > "${AnalysisBaseExternals_DIR}"/lib/python2.7/site-packages/AnalysisBaseExternals_python2.pth
+
 RUN mkdir ${HOME}/data && \
     chown -R --from=root atlas ${HOME} && \
     chown -R --from=root atlas ${HOME}/.jupyter