check_software: check egg vulnerabilities for every used python versions
pkg_resources.Environment only scans packages for the current python version, but the checked software might be using a different python version than the python version used to check software (the slapos python). The checked software might also include packages for multiples python versions.
Compute the list used python packages from the eggs directory and use an Environment for each python version, this way we check all python versions and also when slapos python and software python are different.