Initializes the exporter rpc stream.

def _initialize(self, request):
        """Initializes the exporter rpc stream."""

        # Add node information on the first request dispatched on a stream.
        request.node.MergeFrom(self._node)
        request.resource.MergeFrom(self._resource)
        self._initial_request = request

        self._rpc.open()
        self._initialized = True