title: Wait for callback in createWriteStreamToBlockBlob
body: <p>I'm trying to pipe a stream to Azure's createWriteStreamToBlockBlob but I can't get it to wait until the callback returns before piping to the next part. I need the callback to return before the stream gets to firstLine. Both the blobStream stream and firstLine stream end before the callback.</p>
  
  <pre><code>var blobStream = blobService.createWriteStreamToBlockBlob(config.STORAGE_CONTAINER, _blobFilePath,
          function(err, result){
              console.log(result);
      })
      .on("end", function() {
          console.log("finished");
      })
  
  busboy
      .on('file', function(fieldname, file, filename, encoding, mimetype) {
          file
          .pipe(blobStream)
          .pipe(firstLine)
      })
  </code></pre>