Merge branch 'force-slc6-conda-env' into 'master'

Enforce a specific conda environment for slc6 builds

See merge request !182

prepare_env.sh

@@ -38,6 +38,12 @@ fi
 
 conda_exe=/cvmfs/lhcbdev.cern.ch/conda/miniconda/${conda_arch}/prod/condabin/conda
 
+case "$platform" in
+    *slc6* )
+        export env_hash=d793e9f5b9f35ede449593454325378b56dfde173d823ea6e978b81e5bcba3af
+        ;;
+esac
+
 # Check if we have an externally provided conda environment hash
 if [ -z "$env_hash" ] ; then
   # otherwise we get the default from LHCbNightlyConf