ART is being removed from branches. The latest version (1.0.7) is availab]e via "lsetup art"
setupATLAS asetup <nightly> lsetup art
The ART EOS path is now added to the External/AtlasDataArea/AtlasDataAreaEnvironmentConfig.cmake.in.
Adding @emoyse, @wlampl, @jcatmore, @akraszna