Cherry pick of "Merge branch 'AthDerivationExternalsFix-1.0-20170531' into '1.0'" into master
Fix the python setup in externals packages, 1.0 branch (2017.05.31.)
See merge request !56 (merged)
Fix the python setup in externals packages, 1.0 branch (2017.05.31.)
See merge request !56 (merged)