tools/kvm_stat: add '-f help' to get the available event list

    @staticmethod

    def is_field_wanted(fields_filter, field):

        """Indicate whether field is valid according to fields_filter."""

        if not fields_filter:

        if not fields_filter or fields_filter == "help":

            return True

        return re.match(fields_filter, field) is not None

                         action='store',

                         default=DEFAULT_REGEX,

                         dest='fields',

                         help='fields to display (regex)',

                         help='''fields to display (regex)

                                 "-f help" for a list of available events''',

                         )

    optparser.add_option('-p', '--pid',

                         action='store',

    stats = Stats(options)

    if options.fields == "help":

        event_list = "\n"

        s = stats.get()

        for key in s.keys():

            if key.find('(') != -1:

                key = key[0:key.find('(')]

            if event_list.find('\n' + key + '\n') == -1:

                event_list += key + '\n'

        sys.stdout.write(event_list)

        return ""

    if options.log:

        log(stats)

    elif not options.once: