Corrupted cache causes `bento check` failure

[dlukeomalley]

Overview

Ran bento check with a corrupted cache. Bento fails to parse the cache and hard fails, telling me to run bento init --clean which addresses a different problem.

Current Behavior

[ERROR] 2948.322057723999 root:tool_runner - Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/bento/tool.py", line 259, in results
    violations = self.parser().parse(raw)
  File "/usr/local/lib/python3.7/site-packages/bento/extra/bandit.py", line 201, in parse
    results: Dict[str, List[Dict[str, Any]]] = json.loads(tool_output)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/__init__.py", line 348, in loads
    return _default_decoder.decode(s)
  File "/usr/local/Cellar/python/3.7.3/Frameworks/Python.framework/Versions/3.7/lib/python3.7/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())

Traceback (most recent call last):
  File "/usr/local/lib/python3.7/site-packages/bento/tool_runner.py", line 261, in _setup_and_run_single_tool
    results = self._run_single_tool(bar, ix, tool, baseline)
  File "/usr/local/lib/python3.7/site-packages/bento/tool_runner.py", line 230, in _run_single_tool
    tool.tool_id(), tool.results(self.paths, self.use_cache), baseline
  File "/usr/local/lib/python3.7/site-packages/bento/tool.py", line 262, in results
    f"Could not parse output of '{self.tool_id()}':\n{raw}", e
Exception: ("Could not parse output of 'bandit':\n", JSONDecodeError('Expecting value: line 1 column 1 (char 0)'))

Steps to Reproduce

1. Corrupt the cache
2. bento check

Possible Solution

Add try/catch handling around cache parsing. Either notify of corrupted cache or just automatically delete the cache.

Additional Context

Bento version (run bento --version): 0.8.0b9