Automatically resume interrupted resumable uploads

[coryan]

That is the point of using resumable uploads.

The client should resume the upload if it is interrupted. The client must query the status of the upload, and start from the last byte received.

Note that when the client is reading from a source that cannot be rewound, then the client must buffer enough data to resume the upload. For HTTP, this implies some limited buffer, and PUTs, and stalling until the previous PUT returns successfully. For BidiStreamingWrite, this can be better, with periodic commits and periodic flushing of the buffer.