Turn verbose Kani run into JSON

Given a run of Kani on the standard library with `--verbose` (and,
typically, `autoharness`) enabled this produces a machine-processable
JSON result via
```
python3 log_parser.py \
  --kani-list-file kani-list.json \
  --analysis-results-dir std_lib_analysis/results/ \
  verification.log -o results.json
```
where each entry in the resulting JSON array is of the form
```
{
  "thread_id": int,
  "result": {
    "harness": string,
    "is_autoharness": bool,
    "autoharness_result": string,
    "with_contract": bool,
    "crate": string,
    "function": string,
    "function_safeness": string,
    "file_name": string,
    "n_failed_properties": int,
    "n_total_properties": int,
    "result": string,
    "time": string,
    "output": array
  }
}
```
With the help of `jq` one can then conveniently compute various metrics,
e.g.,
```
jq 'map(select(.result.result == "SUCCESSFUL" and
               .result.is_autoharness == true and
               .result.crate == "core" and
               .result.function_safeness == "unsafe" and
               .result.with_contract == true)) | length' results.json
```
to find the number of successfully-verified contracts of unsafe
functions in crate `core` that were verified using automatically
generated harnesses.

Author: tautschnig