Workarounds for python 3.5

On python 3.5, for each request where SSL authentication fail, even
though application seem functional, a traceback is logged in the log
file.
This makes tests asserting the last log line fail because the last line
is not the access log line, it's the last line of the traceback.

On python >= 3.6, such tracebacks are not logged, so we don't try to fix
this issue but just workaround this for python 3.5. We'll drop this
patch once we stop supporting python 3.5