added definition files for testing with mpich mpi - they generally fail on Grid5000 nodes even with libhdf5-mpich-dev etc installed

adding CentOS8 singularity scripts for Damaris build with prebuild paraview5.9. Adding OPM git update script and build shell functions

separate directories for Ubuntu and CentOS7 recipies. Using a script to source env vars that can propagate through multi-stage builds