Refactor processUpload function fileUtils

[dylankb]

We pass the callback parameter in processUpload down to about four additional methods. It would be nice if we could make this part of the fileUtils a bit easier to read.

[dylankb]

// A long lived callback
processUpload ->(callback)  ->
                                addManifestToFile -> callback ->
                                           |                          addShardsToManifest -> callback->
                              generateManifest                                           readable.on('end () => fileSystem.write
                                                                                                                          |
			                                                                               callback('$dir/$manifestName')