Introduce %py3_check_import
    
    With $PATH and $PYTHONPATH set to the %buildroot,
    the macro tries to import the given Python 3 module(s).
    Useful as a smoke test in %check when ruining tests is not feasible.
    Accepts spaces or commas as separators.
    
    Backport of https://src.fedoraproject.org/rpms/python-rpm-macros/c/c2305ea3