add 'dune-py' to end of the cache directory name
Add 'dune-py' to the end of the path name if the directory is provided via the DUNE_PY_DIR environment variable. This avoids bad things happening when a user just uses $HOME instead of $HOME/dune-py
Add 'dune-py' to the end of the path name if the directory is provided via the DUNE_PY_DIR environment variable. This avoids bad things happening when a user just uses $HOME instead of $HOME/dune-py