Testing environments for Htool

Eight environments are defined via Docker images to test Htool with several MPI implementations:

• Ubuntu with clang and OpenMPI
• Ubuntu with clang and MPICH
• Ubuntu with gcc and OpenMPI
• Ubuntu with gcc and MPICH
• Debian with clang and OpenMPI
• Debian with clang and MPICH
• Debian with gcc and OpenMPI
• Debian with gcc and MPICH

The Docker images can be pulled from Docker Hub. We use GitHub Action to build and push these images to Docker Hub.