DefaultCheckstyleExecutor should be a failure, not an error

[elharo]

Affected version

HEAD

Bug description

Resolve this todo in DefaultCheckstyleExecutor

            if (request.isFailsOnError()) {
                // TODO: should be a failure, not an error. Report is not meant to
                // throw an exception here (so site would
                // work regardless of config), but should record this information
                throw new CheckstyleExecutorException(message.toString());
            }