Reset kvstore.

def _reset_kvstore(self):
        """Reset kvstore."""
        if self._kvstore and 'dist' in self._kvstore.type:
            raise RuntimeError("Cannot reset distributed KVStore.")
        self._kv_initialized = False
        self._kvstore = None
        self._distributed = None
        self._update_on_kvstore = None
        self._params_to_init = [param for param in self._params]