Create a tenant. Currently nothing can be set (to be fixed after the master
        version of Hawkular-Metrics has fixed implementation.

        :param retentions: A set of retention settings, see Hawkular-Metrics documentation for more info

def create_tenant(self, tenant_id, retentions=None):
        """
        Create a tenant. Currently nothing can be set (to be fixed after the master
        version of Hawkular-Metrics has fixed implementation.

        :param retentions: A set of retention settings, see Hawkular-Metrics documentation for more info
        """
        item = { 'id': tenant_id }
        if retentions is not None:
            item['retentions'] = retentions

        self._post(self._get_tenants_url(), json.dumps(item, indent=2))