Comment 4 for bug 1827775

In python3 SafeConfigParser was renamed to ConfigParser and the default
for duplicate options default to true [1]. In case of nova it is valid to
have duplicate option lines, e.g. passthrough_whitelist which leads to
issues reading the nova.conf

The proposed patch from #3 will allow multiple same options in nova.conf for
python3.

[1] https://docs.python.org/3/library/configparser.html#configparser.ConfigParser