The newer version of benchmark upgrade added a "host_name" field to the json report. It looks like combine_benchmark_results.py parses a json output document emitted by the benchmark run. Unfortunately it can't tolerate additional elements that might be present in that document. I think that's a future-proofing bug in combine_benchmark_results.py. I'll try to fix it.

Addressing this so that upgrades to benchmark that add extra info fields without changing the old fields don't break our analysis tools.