Refresh druid datasources

def refresh_druid(datasource, merge):
    """Refresh druid datasources"""
    session = db.session()
    from superset.connectors.druid.models import DruidCluster
    for cluster in session.query(DruidCluster).all():
        try:
            cluster.refresh_datasources(datasource_name=datasource,
                                        merge_flag=merge)
        except Exception as e:
            print(
                "Error while processing cluster '{}'\n{}".format(
                    cluster, str(e)))
            logging.exception(e)
        cluster.metadata_last_refreshed = datetime.now()
        print(
            'Refreshed metadata from cluster '
            '[' + cluster.cluster_name + ']')
    session.commit()