Refresh metadata of all datasources in the cluster
        If ``datasource_name`` is specified, only that datasource is updated

def refresh_datasources(
            self,
            datasource_name=None,
            merge_flag=True,
            refreshAll=True):
        """Refresh metadata of all datasources in the cluster
        If ``datasource_name`` is specified, only that datasource is updated
        """
        ds_list = self.get_datasources()
        blacklist = conf.get('DRUID_DATA_SOURCE_BLACKLIST', [])
        ds_refresh = []
        if not datasource_name:
            ds_refresh = list(filter(lambda ds: ds not in blacklist, ds_list))
        elif datasource_name not in blacklist and datasource_name in ds_list:
            ds_refresh.append(datasource_name)
        else:
            return
        self.refresh(ds_refresh, merge_flag, refreshAll)