Add tests for executables

This requires that the import tests are run with python3, because otherwise the popen timeout doesn't exist.

It finds all executables in the bin folder for packages that have python/*/site-packages and tries to run them with --help/-h/(nothing) if any returns with code 0 the test is successful. I already ignore a number of executables because they return non-zero for all those cases. Some executables are not working because of missing dependencies.

This needs sft/lcgcmake!939 (merged)