Python 2 ElementTree opened the MB response through the StringIO file adapter,
read the encoding parameter in the xml file and gave unicode output
or ascii if that was enough.
Python 2 ElementTree does not seem to support unicode input.
Python 3 StringIO only supports unicode input.
So we decode from bytes to unicode just for Python 3.
Signed-off-by: Johannes Dewender <github@JonnyJD.net>