Use nonstandardlib for purelib definition (#1609492)
    
    The purelib and platlib were both defined to /usr/lib64/python on
    64bits systems. This is because:
    
        >>> get_python_lib(standard_lib=1, plat_specific=0)
        '/usr/lib64/python3.7'
    
        >>> get_python_lib(standard_lib=1, plat_specific=1)
        '/usr/lib64/python3.7'
    
        >>> get_python_lib(standard_lib=0, plat_specific=0)
        '/usr/lib/python3.7/site-packages'
    
        >>> get_python_lib(standard_lib=0, plat_specific=1)
        '/usr/lib64/python3.7/site-packages'
    
    So now we use standard_lib=0 to get the site-packages base path
    from /usr/lib and not /usr/lib64.
    
    Fixes https://bugzilla.redhat.com/show_bug.cgi?id=1609492