Add better error logging on smartctl exec failure

We will now log a warning if smartctl path passed via command line is invalid.

Signed-off-by: Piotr Dobrowolski <admin@tastycode.pl>

readjson.go

@@ -85,6 +85,9 @@ func readSMARTctlDevices(logger log.Logger) gjson.Result {
 			level.Warn(logger).Log("msg", "S.M.A.R.T. output reading error", "err", err)
 			return gjson.Result{}
 		}
+	} else if err != nil {
+		level.Warn(logger).Log("msg", "S.M.A.R.T. output reading error", "err", err)
+		return gjson.Result{}
 	}
 	return parseJSON(string(out))
 }