Chutney doesn't use python3 if a "python2" binary exists, and fails if it uses python3 anyway.
In the "chutney" shell script, the search list for python binaries is:
binaries="python2 python"
This means that even if python3 is installed as "python", chutney will use python2 instead.
This mistake has led us to accumulate a bunch of python3 incompatibilities.