Reporting should not die on old experiment outputs about chaostoolkit-reporting HOT 1 CLOSED

Trace from seeing this:

chaos report --export-format=html5 chaos-report.json report.html
Traceback (most recent call last):
File "/Users/russellmiles/.venvs/chaostk/bin/chaos", line 11, in
sys.exit(cli())
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/click/core.py", line 722, in call
return self.main(*args, **kwargs)
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/click/core.py", line 697, in main
rv = self.invoke(ctx)
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/click/core.py", line 1066, in invoke
return _process_result(sub_ctx.command.invoke(sub_ctx))
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/click/core.py", line 895, in invoke
return ctx.invoke(self.callback, **ctx.params)
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/click/core.py", line 535, in invoke
return callback(*args, **kwargs)
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/chaosreport/cli.py", line 20, in report
generate_report(journal, report, export_format)
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/chaosreport/init.py", line 66, in generate_report
report = template.render(journal)
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/jinja2/asyncsupport.py", line 76, in render
return original_render(self, *args, **kwargs)
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/jinja2/environment.py", line 1008, in render
return self.environment.handle_exception(exc_info, True)
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/jinja2/environment.py", line 780, in handle_exception
reraise(exc_type, exc_value, tb)
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/jinja2/_compat.py", line 37, in reraise
raise value.with_traceback(tb)
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/chaosreport/template/index.md", line 41, in top-level template code
The steady state was {%if steady_states.before.steady_state_met %} verified {% else %} not verified. {% endif %}
File "/Users/russellmiles/.venvs/chaostk/lib/python3.6/site-packages/jinja2/environment.py", line 430, in getattr
return getattr(obj, attribute)
jinja2.exceptions.UndefinedError: 'steady_states' is undefined

from chaostoolkit-reporting.