message: test: Add bitcoin-util tests
diff: [
  + { "exec": "./bitcoin-util",
  + "args": ["foo"],
  + "return_code": 1,
  + "error_txt": "Error parsing command line arguments: Invalid command 'foo'",
  + "description": ""
  + },
  + { "exec": "./bitcoin-util",
  + "args": ["help"],
  + "return_code": 1,
  + "error_txt": "Error parsing command line arguments: Invalid command 'help'",
  + "description": "`help` raises an error. Use `-help`"
  + },
  + { "exec": "./bitcoin-util",
  + "args": ["grind"],
  + "return_code": 1,
  + "error_txt": "Must specify block header to grind",
  + "description": ""
  + },
  + { "exec": "./bitcoin-util",
  + "args": ["grind", "1", "2"],
  + "return_code": 1,
  + "error_txt": "Must specify block header to grind",
  + "description": ""
  + },
  + { "exec": "./bitcoin-util",
  + "args": ["grind", "aa"],
  + "return_code": 1,
  + "error_txt": "Could not decode block header",
  + "description": ""
  + },
  { "exec": "./bitcoin-tx",
  "args": ["-create", "nversion=1"],
  "output_cmp": "blanktxv1.hex",
  