This method should fill up `_machines_cache` from scratch.
        It could happen only in two cases:
        1. During class initialization
        2. When all etcd members failed

def _load_machines_cache(self):
        """This method should fill up `_machines_cache` from scratch.
        It could happen only in two cases:
        1. During class initialization
        2. When all etcd members failed"""

        self._update_machines_cache = True

        if 'srv' not in self._config and 'host' not in self._config and 'hosts' not in self._config:
            raise Exception('Neither srv, hosts, host nor url are defined in etcd section of config')

        self._machines_cache = self._get_machines_cache_from_config()

        # Can not bootstrap list of etcd-cluster members, giving up
        if not self._machines_cache:
            raise etcd.EtcdException

        # After filling up initial list of machines_cache we should ask etcd-cluster about actual list
        self._base_uri = self._next_server()
        self._refresh_machines_cache()

        self._update_machines_cache = False
        self._machines_cache_updated = time.time()