preparation for whatwg stream on blob.stream() #1091

We want to support the real stream at some point and don't have to care whether or not it's a node stream or a blob stream

I think we need change that to this:

 // Body is blob 
 if (isBlob(body)) { 
- 	body = body.stream(); 
+       body = stream.Readable.from(body.stream());
 } 

I where namely thinking of if we should scale down fetch-blob's Blob.prototype.stream function into returning a partial piece of the whatwg stream (which is the async iterator that yields uint8arrays)