returns a string.
        :param dk_api: -- api object
        :param kitchen: string
        :param period: integer
        :rtype: string

def watch_active_servings(dk_api, kitchen, period):
        """
        returns a string.
        :param dk_api: -- api object
        :param kitchen: string
        :param period: integer
        :rtype: string
        """
        print 'period', period

        # try:
        #     p = int(period)
        # except ValueError:
        #     return 'DKCloudCommand.watch_active_servings requires an integer for the period'
        if period <= 0:
            return 'DKCloudCommand.watch_active_servings requires a positive period'

        DKActiveServingWatcherSingleton().set_sleep_time(period)
        DKActiveServingWatcherSingleton().set_api(dk_api)
        DKActiveServingWatcherSingleton().set_kitchen(kitchen)
        DKActiveServingWatcherSingleton().start_watcher()
        return ""