CERN VM 4 container is chosen for SLC6 platforms
When running with a SLC6 platform the CERN VM 4 container is chosen instead of CERN VM 3:
$ lb-run --container singularity -c x86_64-slc6-gcc49-opt DaVinci/v36r7p6 cat /etc/redhat-release
WARNING: Container does not have an exec helper script, calling 'env' directly
Scientific Linux release 7.6 (Nitrogen)
Would it make more sense to match the platform if we can instead of relying on it's backwards compatibility?
I noticed because this call of DaVinci fails on CentOS 7:
'lb-run' '--unset' 'LD_LIBRARY_PATH' '--unset' 'PYTHONPATH' '--siteroot=/cvmfs/lhcb.cern.ch/lib/' '--allow-containers' '-c' 'best' '--use=AppConfig v3r225' '--use=Det/SQLDDDB v7r11' '--use=ProdConf' 'DaVinci/v36r7p6' 'gaudirun.py' '-T' '$APPCONFIGOPTS/DaVinci/DV-Stripping22-Stripping-Turbo.py' '$APPCONFIGOPTS/DaVinci/DataType-2015.py' '$APPCONFIGOPTS/DaVinci/InputType-DST.py' '$APPCONFIGOPTS/Persistency/Compression-ZLIB-1.py'